Figure 5-1 Rewriting Set Semantics
sendmail implements a general purpose internetwork mail routing facility under the UNIX operating system. It is not tied to any one transport protocol -- its function can be compared to a crossbar switch that relays messages from one domain to another. In the process, it can perform a limited amount of message header editing to put the message into a format that is appropriate for the receiving domain. All of this is done under the control of a configuration file.
Although sendmail is intended to run without the need for monitoring, it has a number of features that may be used to monitor or adjust the operation under unusual circumstances.
| Home |
|---|
The system log is supported by the syslogd(1M) program. All messages from sendmail are logged under the LOG_MAIL facility (except on Ultrix, which does not support facilities in the syslog).
Each line in the system log consists of a timestamp, the name of the machine that generated it (for logging from several machines over the local area network), the word "sendmail:", and a message (This format may vary slightly if your vendor has changed the syntax). Most messages are a sequence of name=value pairs.
The two most common lines are logged when a message is processed. The first logs the receipt of a message; there will be exactly one of these per message. Some fields may be omitted if they do not contain interesting information. Fields are:
| from | The envelope sender address. |
| size | The size of the message in bytes. |
| class | The class (i.e., numeric precedence) of the message. |
| pri | The initial message priority (used for queue sorting). |
| nrcpts | The number of envelope recipients for this message (after aliasing and forwarding). |
| msgid | The message id of the message (from the header). |
| proto | The protocol used to receive this message (e.g., ESMTP or UUCP) |
| relay | The machine from which it was received. |
| to | A comma-separated list of the recipients to this mailer. |
| ctladdr | The "controlling user", that is, the name of the user whose credentials we use for delivery. |
| delay | The total delay between the time this message was received and the time it was delivered. |
| xdelay | The amount of time needed in this delivery attempt (normally indicative of the speed of the connection). |
| mailer | The name of the mailer used to deliver to this recipient. |
| relay | The name of the host that actually accepted (or rejected) this recipient. |
| stat | The delivery status. |
If you have syslogd(1M) or an equivalent installed, you will be able to do logging. There is a large amount of information that can be logged. The log is arranged as a succession of levels. At the lowest level only extremely strange situations are logged. At the highest level, even the most mundane and uninteresting events are recorded for posterity. As a convention, log levels under ten are considered generally "useful;" log levels above 64 are reserved for debugging purposes. Levels from 11-64 are reserved for verbose information that some sites might want.
A complete description of the log levels is given in Section 5.4.6.
| Home |
|---|
You can ask sendmail to log a dump of the open files and the connection cache by sending it a SIGUSR1 signal. The results are logged at LOG_DEBUG priority.
Sometimes a host cannot handle a message immediately. For example, it may be down or overloaded, causing it to refuse connections. The sending host is then expected to save this message in its mail queue and attempt to deliver it later.
Under normal conditions the mail queue will be processed transparently. Howev er, you may find that manual intervention is sometimes necessary. For example, if a major host is down for a period of time the queue may become clogged. Although sendmail ought to recover gracefully when the host comes up, you may find performance unacceptably bad in the meantime.
The contents of the queue can be printed using the mailq command (or by specifying the -bp flag to sendmail):
mailqThis will produce a listing of the queue id's, the size of the message, the date the message entered the queue, and the sender and recipients.
| Home |
|---|
sendmail should run the queue automatically at intervals. The algorithm is to read and sort the queue, and then to attempt to process all jobs in order. When it attempts to run the job, sendmail first checks to see if the job is locked. If so, it ignores the job.
There is no attempt to ensure that only one queue processor exists at any time, since there is no guarantee that a job cannot take forever to process (however, sendmail does include heuristics to try to abort jobs that are taking exceptionally long amounts of time; technically, this violates RFC 821, but is blessed by RFC 1123). Due to the locking algorithm, it is impossible for one job to freeze the entire queue. However, an uncooperative recipient host or a program recipient that never returns can accumulate many processes in your system. Unfortunately, there is no general way to resolve this.
In some cases, you may find that a major host going down for a couple of days may create a prohibitively large queue. This will result in sendmail spending an inordinate amount of time sorting the queue. This situation can be fixed by moving the queue to a temporary location and creating a new queue. The old queue can be run later when the offending host returns to service.
To do this, it is acceptable to move the entire queue directory:
cd /var/spoolYou should then kill the existing daemon (since it will still be processing in the old queue directory) and create a new daemon.
mv mqueue omqueue; mkdir mqueue; chmod 700 mqueue
To run the old mail queue, run the following command:
/usr/ucblib/sendmail -oQ/var/spool/omqueue -qThe -oQ flag specifies an alternate queue directory and the -q flag says to just run every job in the queue. If you wish, you can use the -v flag to watch what is going on.
When the queue is finally emptied, you can remove the directory:
rmdir /var/spool/omqueue
| Home |
|---|
sendmail stores a large amount of information about each remote system it has connected to in memory. It is now possible to preserve some of this information on disk as well, by using the HostStatusDirectory option, so that it may be shared between several invocations of sendmail. This allows mail to be queued immediately or skipped during a queue run if there has been a recent failure in connecting to a remote machine.
Additionally enabling SingleThreadDelivery has the added effect of single-threading mail delivery to a destination. This can be quite helpful if the remote machine is running an SMTP server that is easily overloaded or cannot accept more than a single connection at a time, but can cause some messages to be punted to a future queue run. It also applies to all hosts, so setting this because you have one machine on site that runs some software that is easily overrun can cause mail to other hosts to be slowed down. If this option is set, you probably want to set the MinQueueAge option as well and run the queue fairly frequently; this will cause hosts that are skipped because another sendmail instance is talking to it to be tried again soon.
The disk based host information is stored in a subdirectory of of the mqueue directory called .hoststat (this is the usual value of the HostStatusDirectory option; it can, of course, go anywhere you like in your filesystem). Removing this directory and its subdirectories has an effect similar to the purgestat command and is completely safe. The information in these directories can be perused with the hoststat command, which will indicate the host name, the last access, and the status of that access. An asterisk in the left-most column indicates that a sendmail process currently has the host locked for mail delivery.
The disk based connection information is treated the same way as memory based connection information for the purpose of time-outs. By default, information about host failures is valid for 30 minutes. This can be adjusted with the Timeout.hoststatus option.
The connection information stored on disk may be purged at any time with the purgestat command or by invoking sendmail with the -bH switch. The connection information may be viewed with the hoststat command or by invoking sendmail with the -bh switch.
| Home |
|---|
The alias database exists in two forms. One is a text form, maintained in the file /var/ucblib/aliases. The aliases are of the form
name: name1, name2, ...Only local names may be aliased; e.g.,
eric@prep.ai.MIT.EDU: eric@CS.Berkeley.EDUwill not have the desired effect (except on prep.ai.MIT.EDU, and they probably don't want me. (Actually, any mailer that has the 'A' mailer flag set will permit aliasing; this is normally limited to the local mailer.) Aliases may be continued by starting any continuation lines with a space or a tab. Blank lines and lines beginning with a sharp sign ("#") are comments.
The second form is processed by the ndbm(3X)(The gdbm package probably works as well) library. This form is in the files /var/ucblib/aliases.dir and /var/ucblib/aliases.pag. This is the form that sendmail actually uses to resolve aliases. This technique is used to improve performance.
The control of search order is actually set by the service switch. Essentially, the entry
OAswitch:aliasesis always added as the first alias entry; also, the first alias file name without a class (e.g., without "nis:" on the front) will be used as the name of the file for a "files" entry in the aliases switch. For example, if the configuration file contains
OA/var/ucblib/aliasesand the service switch contains
aliases nis filesthen aliases will first be searched in the NIS database, then in /var/ucblib/aliases.
You can also use NIS-based alias files. For example, the specification:
OA/var/ucblib/aliaseswill first search the /var/ucblib/aliases file and then the map named "mail.aliases" in "my.nis.domain".
OAnis:mail.aliases@my.nis.domain
| Home |
|---|
The DBM version of the database may be rebuilt explicitly by executing the command
newaliases
This is equivalent to giving sendmail the -bi flag:
/usr/ucblib/sendmail -bi
If the RebuildAliases (old D) option is specified in the configuration, sendmail will rebuild the alias database automatically if possible when it is out of date. Auto-rebuild can be dangerous on heavily loaded machines with large alias files; if it might take more than the rebuild time-out (option AliasWait, old a, which is normally five minutes) to rebuild the database, there is a chance that several processes will start the rebuild process simultaneously.
If you have multiple alias databases specified, the -bi flag rebuilds all the database types it understands (for example, it can rebuild NDBM databases but not NIS databases).
If you change sendmail version from 5 to 8, you have to rebuild alias database.
There are a number of problems that can occur with the alias database. They all result from a sendmail process accessing the DBM version while it is only partially built. This can happen under two circumstances: One process accesses the database while another process is rebuilding it, or the process rebuilding the database dies (due to being killed or a system crash) before completing the rebuild.
sendmail has three techniques to try to relieve these problems. First, it ignores interrupts while rebuilding the database. This avoids the problem of someone aborting the process and leaving a partially rebuilt database. Second, it locks the database source file during the rebuild -- but that may not work over NFS or if the file is unwriteable. Third, at the end of the rebuild it adds an alias of the form
@: @(which is not normally legal). Before sendmail will access the database, it checks to ensure that this entry exists. (The AliasWait option is required in the configuration for this action to occur. This should normally be specified.)
If an error occurs on sending to a certain address, say "x", sendmail will look for an alias of the form "owner-x" to receive the errors. This is typically useful for a mailing list where the submitter of the list has no control over the maintenance of the list itself; in this case the list maintainer would be the owner of the list. For example:
unix-wizards: eric@ucbarpa, wnj@monet, nosuchuser,would cause "eric@ucbarpa" to get the error that will occur when someone sends to unix-wizards due to the inclusion of "nosuchuser" on the list.
sam@matisse
owner-unix-wizards: unix-wizards-request
unix-wizards-request: eric@ucbarpa
List owners also cause the envelope sender address to be modified. The contents of the owner alias are used if they point to a single user, otherwise the name of the alias itself is used. For this reason, and to obey Internet conventions, the "owner-" address normally points at the "-request" address; this causes messages to go out with the typical Internet convention of using "list-request" as the return address.
| Home |
|---|
As an alternative to the alias database, any user may put a file with the name ".forward" in his or her home directory. If this file exists, sendmail redirects mail for that user to the list of addresses listed in the .forward file. For example, if the home directory for user "mckusick" has a .forward file with contents:
mckusick@erniethen any mail arriving for "mckusick" will be redirected to the specified accounts.
kirk@calder
Actually, the configuration file defines a sequence of filenames to check. By default, this is the user's .forward file, but can be defined to be more general using the J option. If you change this, you will have to inform your user base of the change; .forward is pretty well incorporated into the collective subconscious.
Several header lines have special interpretations defined by the configuration file. Others have interpretations built into sendmail that cannot be changed without changing the code. These built-ins are described here.
If errors occur anywhere during processing, this header will cause error messages to go to the listed addresses. This is intended for mailing lists.
The Errors-To: header was created in the bad old days when UUCP didn't understand the distinction between an envelope and a header; this was a hack to provide what should now be passed as the envelope sender address. It should go away. It is only used if the UseErrorsTo option is set.
The Errors-To: header is officially discouraged and will be phased out in future releases.
RFC 822 requires at least one recipient field (To:, Cc:, or Bcc: line) in every message. If a message comes in with no recipients listed in the message then sendmail will adjust the header based on the "NoRecipientAction" option. One of the possible actions is to add an "Apparently To:" header line for any recipients it is aware of. This is not put in as a standard recipient line to warn any recipients that the list is not complete.
The Apparently-To: header is non-standard and is not advised.
The Precedence: header can be used as a crude control of message priority. It tweaks the sort order in the queue and can be configured to change the message time-out values.
| Home |
|---|
sendmail supports the IDENT protocol as defined in RFC 1413. Although this enhances identification of the author of an email message by doing a "call back" to the originating system to include the owner of a particular TCP connection in the audit trail it is in no sense perfect; a determined forger can easily spoof the IDENT protocol. The following description is excerpted from RFC 1413:
6. Security ConsiderationsThe information returned by this protocol is at most as trustworthy as the host providing it OR the organization operating the host. For example, a PC in an open lab has few if any controls on it to prevent a user from having this protocol return any identifier the user wants. Likewise, if the host has been compromised the information returned may be completely erroneous and misleading.
The Identification Protocol is not intended as an authorization or access control protocol. At best, it provides some additional auditing information with respect to TCP connections. At worst, it can provide misleading, incorrect, or maliciously incorrect information.
The use of the information returned by this protocol for any purpose other than auditing is strongly discouraged. Specifically, using Identification Protocol information to make access control decisions - either as the primary method (i.e., no other checks) or as an adjunct to other methods may result in a breach of normal host security.
An Identification server may reveal information about users, entities, objects or processes which normally would be considered private. An Identification server provides a service which is akin to the CallerID services provided by some phone companies. Many of the same privacy considerations and arguments that apply to the CallerID service also apply to Identification. If you wouldn't run a "finger" server due to privacy considerations you may not want to run this protocol.
In some cases your system may not work properly with IDENT support due to a bug in the TCP/IP implementation. The symptoms will be that for some hosts the SMTP connection will close almost immediately. If this is true or if you do not want to use IDENT, you should set the IDENT time-out to zero; this will disable the IDENT protocol.
To use domain name service, install /usr/ucblib/sendmail.mx in place of /usr/ucblib/sendmail on the mailhost. Each machine running sendmail.mx must have either /etc/resolv.conf or /etc/named.boot set up properly to allow name resolution or at least a caching server.
| Home |
|---|
The complete list of arguments to sendmail is described in detail in Section 5.6. Some important arguments are described here.
The amount of time between forking a process to run through the queue is defined by the -q flag. If you run with delivery mode set to i or b this can be relatively large, since it will only be relevant when a host that was down comes back up. If you run in q mode it should be relatively short, since it defines the maximum amount of time that a message may sit in the queue. (See also the MinQueueAge option.)
RFC 1123 section 5.3.1.1 says that this value should be at least 30 minutes (although that probably doesn't make sense if you use "queue-only" mode).
If you allow incoming mail over an IPC connection, you should have a daemon running. This should be set by your /etc/inet/rc.inetcmd file using the -bd flag. The -bd flag and the -q flag may be combined in one call:
/usr/ucblib/sendmail -bd -q30mAn alternative approach is to invoke sendmail from inetd(1M) (use the -bs flag to ask sendmail to speak SMTP on its standard input and output). This works and allows you to wrap sendmail in a TCP wrapper program, but may be a bit slower since the configuration file has to be re-read on every message that comes in. If you do this, you still need to have a sendmail running to flush the queue:
/usr/ucblib/sendmail -q30m
In some cases you may find that the queue has gotten clogged for some reason. You can force a queue run using the -q flag (with no value). It is entertaining to use the -v flag (verbose) when this is done to watch what happens:
/usr/ucblib/sendmail -q -vYou can also limit the jobs to those with a particular queue identifier, sender, or recipient using one of the queue modifiers. For example, "-qRberkeley" restricts the queue run to jobs that have the string "berkeley" somewhere in one of the recipient addresses. Similarly, "-qSstring" limits the run to particular senders and "-qIstring" limits it to particular queue identifiers.
There are a fairly large number of debug flags built into sendmail. Each debug flag has a number and a level, where a higher level means to print out more information. The convention is that levels greater than nine are "absurd," i.e., they print out so much information that you wouldn't normally want to see them except in the debugging process. Debug flags are set using the -d option; the syntax is:
| debug-flag: | -d debug-list |
| debug-list: | debug-option [ , debug-option ]* |
| debug-option: | debug-range [ . debug-level ] |
| debug-range: | integer | integer - integer |
| debug-level: | integer |
| -d12 | Set flag 12 to level 1 |
| -d12.3 | Set flag 12 to level 3 |
| -d3-17 | Set flags 3 through 17 to level 1 |
| -d3-17.4 | Set flags 3 through 17 to level 4 |
| Home |
|---|
Options can be overridden using the -o or -O command line flags. For example,
/usr/ucblib/sendmail -oT2msets the T (time-out) option to two minutes for this run only; the equivalent line using the long option name is
/usr/ucblib/sendmail -OTimeout.queuereturn=2mSome options have security implications. sendmail allows you to set these, but relinquishes its setuid root permissions thereafter. (That is, it sets its effective uid to the real uid; thus, if you are executing as root, as from root's crontab file, or during system startup, the root permissions will still be honored.)
An alternative configuration file can be specified using the -C flag; for example,
/usr/ucblib/sendmail -Ctest.cf -oQ/tmp/mqueueuses the configuration file test.cf instead of the default /var/ucblib/sendmail.cf. If the -C flag has no value it defaults to sendmail.cf in the current directory.
sendmail gives up its setuid root permissions when you use this flag, so it is common to use a publicly writeable directory (such as /tmp) as the spool directory (QueueDirectory or Q option) while testing.
Many SMTP implementations do not fully implement the protocol. For example, some PC-based SMTPs do not understand continuation lines in reply codes. These can be very hard to trace. If you suspect such a problem, you can set traffic logging using the -X flag. For example,
/usr/ucblib/sendmail -X /tmp/traffic -bdwill log all traffic in the file /tmp/traffic.
This logs a lot of data very quickly and should NEVER be used during normal operations. After starting up such a daemon, force the errant implementation to send a message to your host. All message traffic in and out of sendmail, including the incoming SMTP traffic, will be logged in this file.
| Home |
|---|
When you build a configuration table, you can do a certain amount of testing using the "test mode" of sendmail. For example, you could invoke sendmail as:
sendmail -bt -Ctest.cfwhich would read the configuration file "test.cf" and enter test mode. In this mode, you enter lines of the form:
rwset addresswhere rwset is the rewriting set you want to use and address is an address to apply the set to. Test mode shows you the steps it takes as it proceeds, finally showing you the address it ends up with. You may use a comma-separated list of rwsets for sequential application of rules to an input. For example:
3,1,21,4 monet:bollardfirst applies ruleset three to the input "monet:bollard." Ruleset one is then applied to the output of ruleset three, followed similarly by rulesets twenty-one and four.
If you need more detail, you can also use the "-d21" flag to turn on more debugging. For example,
sendmail -bt -d21.99turns on an incredible amount of information; a single word address is probably going to print out several pages worth of information.
You should be warned that internally, sendmail applies ruleset 3 to all addresses. In test mode you will have to do that manually. For example, older versions allowed you to use
0 bruce@broadcast.sony.comThis version requires that you use:
3,0 bruce@broadcast.sony.comAs of version 8.7, some other syntaxes are available in test mode:
When HostStatusDirectory is enabled, information about the status of hosts is maintained on disk and can be shared between different instantiations of sendmail. The status of the last connection with each remote host may be viewed with the command:
sendmail -bhThis information may be flushed with the command:
sendmail -bHFlushing the information prevents new sendmail processes from loading it, but does not prevent existing processes from using the status information that they already have.
| Home |
|---|
There are a number of configuration parameters you may want to change, depending on the requirements of your site. Most of these are set using an option in the configuration file. For example, the line "O Timeout.queuereturn=5d" sets option "Timeout.queuereturn" to the value "5d" (five days).
Most of these options have appropriate defaults for the amjority of sites. However, sites having very high mail loads may find they need to tune them as appropriate for their mail load. In particular, sites receiving a large number of small messages delivered to many recipients may need to adjust the parameters dealing with queue priorities.
All versions of sendmail prior to 8.7 had single-character option names. As of 8.7, options have long (multi-character names). Although old short names are still recognized, most new options do not have short equivalents.
This section describes only the options you are most likely to want to modify; read Section 5.5 for more details.
All time intervals are set using a scaled syntax. For example, "10m" represents ten minutes, whereas "2h30m" represents 2.5 hours. The full set of scales is:
s seconds m minutes h hours d days w weeks
The argument to the -q flag specifies how often a sub-daemon will run the queue. This is typically set to between fifteen minutes and one hour. RFC 1123 section 5.3.1.1 recommends that this be at least 30 minutes.
| Home |
|---|
Time-outs all have option names "Timeout.suboption". The recognized suboptions, their default values, and the minimum values allowed by RFC 1123 section 5.3.2 are:
| connect | The time to wait for an SMTP connection to open (the connect(2) system call) [0, unspecified]. If zero, uses the kernel default. In no case can this option extend the time-out longer than the kernel provides, but it can shorten it. This is to get around kernels that provide an exceptionally long connection time-out (90 minutes in one case). |
| iconnect | The same as connect, except it applies only to the initial attempt to connect to a host for a given message [0, unspecified]. The concept is that this should be very short (a few seconds); hosts that are well connected and responsive will be serviced immediately. Hosts that are slow will not hold up other deliveries in the initial delivery attempt. |
| initial | The wait for the initial 220 greeting message [5m, 5m]. |
| helo | The wait for a reply from a HELO or EHLO command [5m, unspecified]. This may require a host name lookup; five minutes is probably a reasonable minimum. |
| mail# | The wait for a reply from a MAIL command [10m, 5m]. |
| rcpt# | The wait for a reply from an RCPT command [1h, 5m]. This should be long, as it could be pointing at a list that takes a long time to expand (see below). |
| datainit# | The wait for a reply from a DATA command [5m, 2m]. |
| datablock# | The wait for reading a data block (that is, the body of the message). [1h, 3m]. This should be long because it also applies to programs piping input to send mail which have no guarantee of promptness. |
| datafinal# | The wait for a reply from the dot terminating a message. [1h, 10m]. If this is shorter than the time actually needed for the receiver to deliver the message, duplicates will be generated. This is discussed in RFC 1047. |
| rset | The wait for a reply from an RSET command [5m, unspecified]. |
| quit | The wait for a reply from a QUIT command [2m, unspecified]. |
| misc | The wait for a reply from miscellaneous (but short) commands such as NOOP (no-operation) and VERB (go into verbose mode). [2m, unspecified]. |
| command# | In server SMTP, the time to wait for another command. [1h, 5m]. |
| ident | The time-out waiting for a reply to an IDENT query [30s (on some systems the default is zero to turn the protocol off entirely), unspecified]. |
| Home |
|---|
Many of the RFC 1123 minimum values may well be too short. sendmail was designed to the RFC 822 protocols, which did not specify read time-outs; hence, versions of sendmail prior to version 8.1 did not guarantee prompt replies to messages. In particular, an "RCPT" command specifying a mailing list will expand and verify the entire list; a large list on a slow system may easily take more than five minutes. (This verification includes looking up every address with the name server; this involves network delays, and can in some cases can be considerable.) I recommend a one-hour time-out -- since a communications failure during the RCPT phase is rare, a long time-out is not onerous and may ultimately help reduce network load and duplicated messages.
For example, the lines:
set the server SMTP command time-out to 25 minutes and the input data block time-out to three hours.O Timeout.command=25m
O Timeout.datablock=3h
After sitting in the queue for a few days, a message will time out. This is to ensure that the sender is aware of the inability to send a message. The time-out is typically set to five days. It is sometimes considered convenient to also send a warning message if the message is in the queue longer than a few hours (assuming you normally have good connectivity; if your messages normally took several hours to send you wouldn't want to do this because it wouldn't be an unusual event). These time-outs are set using the Timeout.queuereturn and Timeout.queue warn options in the configuration file (previously both were set using the T option).
Since these options are global, and since you cannot know a priori how long another host outside your domain will be down, a five-day time-out is recommended. This allows a recipient to fix the problem even if it occurs at the beginning of a long weekend. RFC 1123 section 5.3.1.1 says that this parameter should be "at least 4-5 days".
The Timeout.queuewarn value can be piggybacked on the T option by indicating a time after which a warning message should be sent; the two time-outs are separated by a slash. For example, the line
OT5d/4hcauses email to fail after five days, but a warning message will be sent after four hours. This should be large enough that the message will have been tried several times.
| Home |
|---|
By setting the ForkEachJob (Y) option, sendmail will fork before each individual message while running the queue. This will prevent sendmail from consuming large amounts of memory, so it may be useful in memory-poor environments. However, if the ForkEachJob option is not set, sendmail will keep track of hosts that are down during a queue run, which can improve performance dramatically.
If the ForkEachJob option is set, sendmail cannot use connection caching.
Every message is assigned a priority when it is first instantiated, consisting of the message size (in bytes) offset by the message class (which is determined from the Precedence: header) times the "work class factor" and the number of recipients times the "work recipient factor." The priority is used to order the queue. Higher numbers for the priority mean that the message will be processed later when running the queue.
The message size is included so that large messages are penalized relative to small messages. The message class allows users to send "high priority" messages by including a "Precedence:" field in their message; the value of this field is looked up in the P lines of the configuration file. Since the number of recipients affects the amount of load a message presents to the system, this is also included into the priority.
The recipient and class factors can be set in the configuration file using the RecipientFactor (y) and ClassFactor (z) options respectively. They default to 30000 (for the recipient factor) and 1800 (for the class factor). The initial priority is:
pri = msgsize - (class * ClassFactor) + (nrcpt * RecipientFactor)(Remember, higher values for this parameter actually mean that the job will be treated with lower priority.)
The priority of a job can also be adjusted each time it is processed (that is, each time an attempt is made to deliver it) using the "work time factor," set by the RetryFactor (Z) option. This is added to the priority, so it normally decreases the precedence of the job, on the grounds that jobs that have failed many times will tend to fail again in the future. The RetryFactor option defaults to 90000.
| Home |
|---|
For drastic cases, the RefuseLA (X) option defines a load average at which sendmail will refuse to accept network connections. Locally generated mail (including incoming UUCP mail) is still accepted.
| i | deliver interactively (synchronously) |
| b | deliver in background (asynchronously) |
| q | queue only (don't deliver) |
| d | defer delivery attempts (don't deliver) |
If you run in mode "q" (queue only), "d" (defer), or "b" (deliver in background) sendmail will not expand aliases and follow .forward files upon initial receipt of the mail. This speeds up the response to RCPT commands. Mode "i" cannot be used by the SMTP server.
| Home |
|---|
The level of logging can be set for sendmail. The default using a standard configuration table is level 9. The levels are as follows:
| 0 | No logging. |
| 1 | Serious system failures and potential security problems. |
| 2 | Lost communications (network problems) and protocol failures. |
| 3 | Other serious failures. |
| 4 | Minor failures. |
| 5 | Message collection statistics. |
| 6 | Creation of error messages, VRFY and EXPN commands. |
| 7 | Delivery failures (host or user unknown, etc.). |
| 8 | Successful deliveries and alias database rebuilds. |
| 9 | Messages being deferred (due to a host being down, etc.). |
| 10 | Database expansion (alias, forward, lookups). |
| 12 | Log all incoming and outgoing SMTP commands. |
| 20 | Logs attempts to run locked queue files. These are not errors, but can be useful to note if your queue appears to be clogged. |
| 30 | Lost locks (only if using lockf instead of flock). |
The modes used for files depend on what functionality you want and the level of security you require.
sendmail can safely be made setuid to root. At the point where it is about to exec(2) a mailer, it checks to see if the userid is zero; if so, it resets the userid and groupid to a default (set by the u and g options). (This can be overridden by setting the S flag to the mailer for mailers that are trusted and must be called as root.) However, this will cause mail processing to be accounted to root rather than to the user sending the mail.
If you don't make sendmail setuid to root, it will still run but you lose a lot of functionality and a lot of privacy, since you'll have to make the queue directory world-readable. You could also make sendmail setuid to some pseudo-user (e.g., create a user called "sendmail" and make sendmail setuid to that) which will fix the privacy problems but not the functionality issues. Also, this isn't a guarantee of security: for example, root occasionally sends mail, and the daemon often runs as root.
At Berkeley we have the alias database (/var/ucblib/aliases*) mode 644. While this is not as flexible as if the database were more (e.g., 666), it avoids potential security problems with a globally writeable database.
The database that sendmail actually used is represented by the two files aliases.dir and aliases.pag (both in /var/ucblib) (or aliases.db if you are running with the new Berkeley database primitives). The mode on these files should match the mode on /var/ucblib/aliases. If aliases is writeable and the DBM files (aliases.dir and aliases.pag) are not, users will be unable to reflect their desired changes through to the actual database. However, if aliases is read-only and the DBM files are writeable, a slightly sophisticated user can arrange to steal mail anyway.
If your DBM files are not writeable by the world or you do not have auto-rebuild enabled (with the AutoRebuildAliases option), then you must be careful to reconstruct the alias database each time you change the text version:
newaliasesIf this step is ignored or forgotten any intended changes will also be ignored or forgotten.
| Home |
|---|
When processing the queue, sendmail will try to keep the last few open connections open to avoid startup and shutdown costs. This only applies to IPC connections.
When trying to open a connection the cache is first searched. If an open connection is found, it is probed to see if it is still active by sending an RSET command. It is not an error if this fails; instead, the connection is closed and reopened.
Two parameters control the connection cache. The ConnectionCacheSize (k) option defines the number of simultaneous open connections that will be permitted. If it is set to zero, connections will be closed as quickly as possible. The default is one. This should be set as appropriate for your system size; it will limit the amount of system resources that sendmail will use during queue runs. Never set this higher than 4.
The ConnectionCacheTimeout (K) option specifies the maximum time that any cached con nection will be permitted to idle. When the idle time exceeds this value the connection is closed. This number should be small (under ten minutes) to prevent you from grabbing too many resources from other hosts. The default is five minutes.
| Home |
|---|
The ResolverOptions (I) option allows you to tweak name server options. The command line takes a series of flags as documented in resolver(3N) (with the leading "RES_" deleted). Each can be preceded by an optional '+' or '-'. For example, the line
O ResolverOptions=+AAONLY -DNSRCHturns on the AAONLY (accept authoritative answers only) and turns off the DNSRCH (search the domain path) options. Most resolver libraries default DNSRCH, DEFNAMES, and RECURSE flags on and all others off. You can also include "HasWildcardMX" to specify that there is a wild card MX record matching your domain; this turns off MX matching when canonifying names, which can lead to inappropriate canonifications.
Version level 1 configurations turn DNSRCH and DEFNAMES off when doing delivery lookups, but leave them on everywhere else. Version 8 of sendmail ignores them when doing canonification lookups (that is, when using $[ ... $]), and always does the search. If you don't want to do automatic name extension, don't call $[ ... $].
The search rules for $[ ... $] are somewhat different than usual. If the name being looked up has at least one dot, it always tries the unmodified name first. If that fails, it tries the reduced search path, and lastly tries the unmodified name (but only for names without a dot, since names with a dot have already been tried). This allows names such as "utc.CS" to match the site in Czechoslovakia rather than the site in your local Computer Science department. It also prefers A and CNAME records over MX records -- that is, if it finds an MX record it makes note of it, but keeps looking. This way, if you have a wildcard MX record matching your domain, it will not assume that all names match.
| Home |
|---|
Some sites mount each user's home directory from a local disk on their workstation, so that local access is fast. However, the result is that .forward file lookups are slow. In some cases, mail can even be delivered on machines inappropriately because of a file server being down. The performance can be especially bad if you run the automounter.
The ForwardPath (J) option allows you to set a path of forward files. For example, the config file line
O ForwardPath=/var/forward/$u:$z/.forward.$wwould first look for a file with the same name as the user's login in /var/forward; if that is not found (or is inaccessible) the file ".forward.machinename" in the user's home directory is searched. A truly perverse site could also search by sender by using $r, $s, or $f.
If you create a directory such as /var/forward, it should be mode 1777 (that is, the sticky bit should be set). Users should create the files mode 644.
On systems that have one of the system calls in the statfs(2) family , you can specify a minimum number of free blocks on the queue filesystem using the Min FreeBlocks (b) option. If there are fewer than the indicated number of blocks free on the filesystem on which the queue is mounted the SMTP server will reject mail with the 452 error code. This invites the SMTP client to try again later.
Beware of setting this option too high; it can cause rejection of email when that mail would be processed without difficulty.
| Home |
|---|
To avoid overflowing your system with a large message, the MaxMessageSize option can be set to set an absolute limit on the size of any one message. This will be advertised in the ESMTP dialogue and checked during message collection.
The PrivacyOptions (p) option allows you to set certain "privacy" flags. Actually, many of them don't give you any extra privacy. Instead, they require that client SMTP servers use the HELO command before using certain commands or adding extra headers to indicate possible spoof attempts.
The option takes a series of flag names; the final privacy is the inclusive or of those flags. For example:
O PrivacyOptions=needmailhelo, noexpninsists that the HELO or EHLO command be used before a MAIL command is accepted and disables the EXPN command.
The flags are detailed in Section 5.5.6.
Normally, sendmail deletes the (envelope) sender from any list expansions. For example, if "matt" sends to a list that contains "matt" as one of the members he won't get a copy of the message. If the -m (me too) command line flag, or if the MeToo (m) option is set in the configuration file, this behavior is suppressed. Some sites like to run the SMTP daemon with -m.
| Home |
|---|
This section describes the configuration file in detail.
There is one point that should be made clear: since the configuration file is parsed every time sendmail starts up. the syntax of the configuration file is optimized for this purpose (easy parsing by the system, as opposed to easy reading by the operator, is the goal.) On the "future project" list is a configuration-file compiler.
The configuration file is organized as a series of lines, each of which begins with a single character defining the semantics for the rest of the line. Lines beginning with a space or a tab are continuation lines (although the semantics are not well defined in many places). Blank lines and lines beginning with a sharp symbol ('#') are comments.
The core of address parsing is the rewriting rules. These are an ordered production system. sendmail scans through the set of rewriting rules looking for a match on the left hand side (LHS) of the rule. When a rule matches, the address is replaced by the right hand side (RHS) of the rule.
There are several sets of rewriting rules. Some of the rewriting sets are used internally and must have specific semantics. Other rewriting sets do not have specifically assigned semantics, and may be referenced by the mailer definitions or by other rewriting sets.
The syntax of these two commands are:
SnSets the current ruleset being collected to n. If you begin a ruleset more than once it appends to the old definition.
Rlhs rhs commentsThe fields must be separated by at least one tab character; there may be embedded spaces in the fields. The lhs is a pattern that is applied to the input. If it matches, the input is rewritten to the rhs. The comments are ignored.
Macro expansions of the form $x are performed when the configuration file is read. Expansions of the form $&x are performed at run time using a somewhat less general algorithm. This is intended only for referencing internally defined macros such as $h that are changed at runtime.
| Home |
|---|
The left-hand side of rewriting rules contains a pattern. Normal words are simply matched directly. Metasyntax is introduced using a dollar sign. The metasymbols are:
| $* | Match zero or more tokens |
| $+ | Match one or more tokens |
| $- | Match exactly one token |
| $=x | Match any phrase in class x |
| $~x | Match any word not in class x |
$-:$+is applied to the input:
UCBARPA:ericthe rule will match, and the values passed to the RHS will be:
| $1 | UCBARPA |
| $2 | eric |
| Home |
|---|
When the left-hand side of a rewriting rule matches, the input is deleted and replaced by the right-hand side. Tokens are copied directly from the RHS unless they begin with a dollar sign. Metasymbols are:
| $n | Substitute indefinite token n from LHS |
| $[name$] | Canonicalize name |
| $(map key $@arguments $:default $) | Generalized keyed mapping function |
| $>n | "Call" ruleset n |
| $#mailer | Resolve to mailer |
| $@host | Specify host |
| $:user | Specify user |
A host name enclosed between $[ and $] is looked up in the host database(s) and replaced by the canonical name. (This is actually completely equivalent to $(host hostname$). In particular, a $: default can be used.) For example, "$[ftp$]" might become "ftp.CS.Berkeley.EDU" and "$[[128.32.130.2]$]" would become "vangogh.CS.Berkeley.EDU." sendmail recognizes its numeric IP address without calling the name server and replaces it with its canonical name.
The $( ... $) syntax is a more general form of lookup; it uses a named map instead of an implicit map. If no lookup is found, the indicated default is inserted; if no default is specified and no lookup matches, the value is left unchanged. The arguments are passed to the map for possible use.
The $>n syntax causes the remainder of the line to be substituted as usual and then passed as the argument to ruleset n. The final value of ruleset n then becomes the substitution for this rule. The $> syntax can only be used at the beginning of the right-hand side; it can be only be preceded by $@ or $:.
The $# syntax should only be used in ruleset zero or a subroutine of ruleset zero. It causes evaluation of the ruleset to terminate immediately, and signals to sendmail that the address has completely resolved. The complete syntax is:
$#mailer $@host $:userThis specifies the {mailer, host, user} 3-tuple necessary to direct the mailer. If the mailer is local the host part may be omitted. (You may want to use it for special "per user" extensions. For example, in the address "jgm+f oo@CMU.EDU"; the "+foo" part is not part of the user name, and is passed to the local mailer for local use.) The mailer must be a single word, but the host and user may be multi-part. If the mailer is the built-in IPC mailer, the host may be a colon-separated list of hosts that are searched in order for the first working address (exactly like MX records). The user is later rewritten by the mailer-specific envelope rewriting set and assigned to the $u macro. As a special case, if the mailer specified has the F=@ flag specified and the first character of the $: value is "@", the "@" is stripped off, and a flag is set in the address descriptor that causes sendmail to not do ruleset 5 processing.
Normally, a rule that matches is retried, that is, the rule loops until it fails. An RHS may also be preceded by a $@ or a $: to change this behavior. A $@ prefix causes the ruleset to return with the remainder of the RHS as the value. A $: prefix causes the rule to terminate immediately, but the ruleset to continue; this can be used to avoid continued application of a rule. The prefix is stripped before continuing.
The $@ and $: prefixes may precede a $> spec; for example:
R$+ $: $>7 $1matches anything, passes that to ruleset seven, and continues; the $: is necessary to avoid an infinite loop.
Substitution occurs in the order described, that is, parameters from the LHS are substi tuted, hostnames are canonicalized, "subroutines" are called, and finally $#, $@, and $: are processed.
| Home |
|---|
There are five rewriting sets that have specific semantics. Four of these are related, as depicted by Figure 1.
Ruleset three should turn the address into "canonical form." This form should have the basic syntax:
local-part@host-domain-specRuleset three is applied by sendmail before doing anything with any address.
If no "@" sign is specified, then the host-domain-spec may be appended (box "D" in Figure 1) from the sender address (if the C flag is set in the mailer definition corresponding to the sending mailer).
Ruleset zero is applied after ruleset three to addresses that are going to actually specify recipients. It must resolve to a {mailer, host, user} triple. The mailer must be defined in the mailer definitions from the configuration file. The host is defined into the $h macro for use in the argv expansion of the specified mailer.
Rulesets one and two are applied to all sender and recipient addresses respectively. They are applied before any specification in the mailer definition. They must never resolve.
Ruleset four is applied to all addresses in the message. It is typically used to translate internal to external form.
Figure 5-1 Rewriting Set Semantics
In addition, ruleset 5 is applied to all local addresses (specifically, those that resolve to a mailer with the 'F=5' flag set) that do not have aliases. This allows a last minute hook for local names.
| Home |
|---|
A few extra rulesets are defined as "hooks" that can be defined to get special features. They are all named rulesets. The "check_*" forms all give accept/reject status; falling off the end or returning normally is an accept, and resolving to $#error is a reject.
The check_relay ruleset is called after a connection is accepted. It is passed
client.host.name $| client.host.addresswhere $| is a metacharacter separating the two parts. This ruleset can reject connections from various locations.
The check_mail ruleset is passed the user name parameter of the SMTP MAIL command. It can accept or reject the address.
The check_rcpt ruleset is passed the user name parameter of the SMTP RCPT command. It can accept or reject the address.
The check_compat ruleset is passed
sender-address $| recipient-addresswhere $| is a metacharacter separating the addresses. It can accept or reject mail transfer between these two addresses much like the checkcompat() function.
| Home |
|---|
Some special processing occurs if the ruleset zero resolves to an IPC mailer (that is, a mailer that has "[IPC]" listed as the Path in the M configuration line. The host name passed after "$@" has MX expansion performed; this looks the name up in DNS to find alternate delivery sites.
The host name can also be provided as a dotted quad in square brackets; for example:
[128.32.149.78]This causes direct conversion of the numeric value to a TCP/IP host address.
The host name passed in after the "$@" may also be a colon-separated list of hosts. Each is separately MX expanded and the results are concatenated to make (essentially) one long MX list. The intent here is to create "fake" MX records that are not published in DNS for private internal networks.
As a final special case, the host name can be passed in as a text string in square brackets:
[ucbvax.berkeley.edu]This form avoids the MX mapping. N.B.: This is intended only for situations where you have a network firewall or other host that will do special processing for all your mail, so that your MX record points to a gateway machine; this machine could then do direct delivery to machines within your local domain. Use of this feature directly violates RFC 1123 section 5.3.5: it should not be used lightly.
Macros are named with a single character or with a word in {braces}. Single character names may be selected from the entire ASCII set, but user-defined macros should be selected from the set of uppercase letters only. Lowercase letters and special symbols are used internally. Long names beginning with a lowercase letter or a punctuation character are reserved for use by sendmail, so user-defined long macro names should begin with an uppercase letter.
The syntax for macro definitions is:
Dx valwhere x is the name of the macro (which may be a single character or a word in braces) and val is the value it should have. There should be no spaces given that do not actually belong in the macro value.
Macros are interpolated using the construct $x, where x is the name of the macro to be interpolated. This interpolation is done when the configuration file is read, except in M lines. The special construct $&x can be used in R lines to get deferred interpolation.
Conditionals can be specified using the syntax:
$?x text1 $| text2 $.This interpolates text1 if the macro $x is set, and text2 otherwise. The "else" ($|) clause may be omitted.
Lowercase macro names are reserved to have special semantics, used to pass information in or out of sendmail, and special characters are reserved to provide conditionals, etc. Uppercase names (that is, $A through $Z) are specifically reserved for configuration file authors.
| Home |
|---|
The following macros are defined and/or used internally by sendmail for interpolation into argv's for mailers or for other contexts. The ones marked # are information passed into sendmail. (As of version 8.6, all of these macros have reasonable defaults. Previous versions required that they be defined.) The ones marked ## are information passed both in and out of sendmail, and the unmarked macros are passed out of sendmail but are not otherwise used internally. These macros are:
| $a | The origination date in RFC 822 format. This is extracted from the Date: line. |
| $b | The current date in RFC 822 format. |
| $c | The hop count. This is a count of the number of Received: lines plus the value of the -h command line flag. |
| $d | The current date in UNIX (ctime) format. |
| $e# | (Obsolete; use SmtpGreetingMessage option instead.) The SMTP entry message. This is printed out when SMTP starts up. The first word must be the $j macro as specified by RFC821. Defaults to "$j Sendmail $v ready at $b". Commonly redefined to include the con figuration version number, e.g., "$j Sendmail $v/$Z ready at $b" |
| $f | The envelope sender (from) address. |
| $g | The sender address relative to the recipient. For example, if $f is "foo", $g will be "host!foo", "foo@host.domain", or whatever is appropriate for the receiving mailer. |
| $h | The recipient host. This is set in ruleset 0 from the $# field of a parsed address. |
| $i | The queue id, e.g., "HAA12345". |
| $j## | The "official" domain name for this site. This is fully qualified if the full qualification can be found. It must be redefined to be the fully qualified domain name if your system is not con figured so that information can find it automatically. |
| $k | The UUCP node name (from the uname system call). |
| $l# | (Obsolete; use UnixFromLine option instead.) The format of the UNIX from line. Unless you have changed the UNIX mailbox format, you should not change the default, which is "From $g $d". |
| $m | The domain part of the gethostname return value. Under normal circumstances, $j is equivalent to $w.$m. |
| $n# | The name of the daemon (for error messages). Defaults to "MAILER-DAEMON". |
| $o# | (Obsolete: use OperatorChars option instead.) The set of "operators" in addresses. A list of characters which will be considered tokens and which will separate tokens when doing parsing. For example, if "@" were in the $o macro, then the input "a@b" would be scanned as three tokens: "a," "@," and "b." Defaults to ".:@[]", which is the minimum set necessary to do RFC 822 parsing; a richer set of operators is ".:%@!/[]", which adds support for UUCP, the %-hack, and X.400 addresses. |
| $p | Sendmail's process id. |
| $q# | Default format of sender address. The $q macro specifies how an address should appear in a message when it is defaulted. Defaults to "<$g>". It is commonly redefined to be "$?x$x <$g>$|$g$." or "$g$?x ($x)$.", corresponding to the following two formats:
Eric Allman <eric@CS.Berkeley.EDU>sendmail properly quotes names that have special characters if the first form is used. |
| $r | Protocol used to receive the message. Set from the -p command line flag or by the SMTP server code. |
| $s | Sender's host name. Set from the -p command line flag or by the SMTP server code. |
| $t | A numeric representation of the current time. |
| $u | The recipient user. |
| $v | The version number of the sendmail binary. |
| $w## | The hostname of this site. This is the root name of this host (but see below for caveats). |
| $x | The full name of the sender. |
| $z | The home directory of the recipient. |
| $_ | The validated sender address. |
| ${bodytype} | The message body type (7BIT or 8BITMIME), as determined from the envelope. |
| ${client_addr} | The IP address of the SMTP client. Defined in the SMTP server only. |
| ${client_name} | The host name of the SMTP client. Defined in the SMTP server only. |
| ${client_port} | The port number of the SMTP client. Defined in the SMTP server only. |
| ${envid} | The envelope id passed to sendmail as part of the envelope. |
| ${opMode} | The current operation mode (from the -b flag). |
| Home |
|---|
There are three types of dates that can be used. The $a and $b macros are in RFC 822 format; $a is the time as extracted from the "Date:" line of the message (if there was one), and $b is the current date and time (used for postmarks). If no "Date:" line is found in the incoming message, $a is set to the current time also. The $d macro is equivalent to the $b macro in UNIX (ctime) for mat.
The macros $w, $j, and $m are set to the identity of this host. sendmail tries to find the fully qualified name of the host if at all possible; it does this by calling gethostname(2) to get the current hostname and then passing that to gethostbyname(3N) which is supposed to return the canonical version of that host name (for example, on some systems gethostname might return "foo" which would be mapped to "foo.bar.com" by gethostbyname). Assuming this is successful, $j is set to the fully qualified name and $m is set to the domain part of the name (everything after the first dot). The $w macro is set to the first word (everything before the first dot) if you have a level 5 or higher configuration file; otherwise, it is set to the same value as $j. If the canonification is not successful, it is imperative that the config file set $j to the fully qualified domain name (older versions of sendmail didn't pre-define $j at all, so up until 8.6, config files always had to define $j).
The $f macro is the id of the sender as originally determined; when mailing to a specific host the $g macro is set to the address of the sender relative to the recipient. For example, if I send to "bollard@matisse.CS.Berkeley.EDU" from the machine "vangogh.CS.Berkeley.EDU" the $f macro will be "eric" and the $g macro will be "eric@vangogh.CS.Berkeley.EDU."
The $x macro is set to the full name of the sender. This can be determined in several ways. It can be passed as flag to sendmail. It can be defined in the NAME environment variable. The third choice is the value of the "Full-Name:" line in the header if it exists, and the fourth choice is the comment field of a "From:" line. If all of these fail, and if the message is being originated locally, the full name is looked up in the /etc/passwd file.
When sending, the $h, $u, and $z macros get set to the host, user, and home directory (if local) of the recipient. The first two are set from the $@ and $: parts of the rewriting rules, respectively.
The $p and $t macros are used to create unique strings (e.g., for the "Message-Id:" field). The $i macro is set to the queue id on this host; if put into the timestamp line it can be extremely useful for tracking messages. The $v macro is set to be the version number of sendmail; this is nor mally put in timestamps and has been proven extremely useful for debugging.
The $c field is set to the "hop count," i.e., the number of times this message has been processed. This can be determined by the -h flag on the command line or by counting the timestamps in the message.
The $r and $s fields are set to the protocol used to communicate with sendmail and the sending hostname. They can be set together using the -p command line flag or separately using the -M or -oM flags.
The $_ is set to a validated sender host name. If the sender is running an RFC 1413 compliant IDENT server and the receiver has the IDENT protocol turned on, it will include the user name on that host.
The ${client_name}, ${client_addr}, and ${client_port} macros are set to the name, address, and port number of the SMTP client who is invoking sendmail as a server. These can be used in the check_* rulesets (using the $& deferred evaluation form, of course!).
| Home |
|---|
Classes of phrases may be defined to match on the left-hand side of rewriting rules, where a "phrase" is a sequence of characters that do not contain space characters. For example a class of all local names for this site might be created so that attempts to send to oneself can be eliminated. These can either be defined directly in the configuration file or read in from another file. Classes are named as a single letter or a word in {braces}. Class names beginning with lowercase letters and special characters are reserved for system use. Classes defined in config files may be given names from the set of uppercase letters for short names or beginning with an uppercase letter for long names.
The syntax is:
Cc phrase1 phrase2...The first form defines the class c to match any of the named words. It is permissible to split them among multiple lines; for example, the two forms:
Fc file
CHmonet ucbmonetand
CHmonetare equivalent. The "F" form reads the elements of the class c from the named file.
CHucbmonet
Elements of classes can be accessed in rules using $= or $~. The $~ (match entries not in class) only matches a single word; multi-word entries in the class are ignored in this context.
Some classes have internal meaning to sendmail:
| $=e | contains the Content-Transfer-Encodings that can be 8*7 bit encoded. It is predefined to contain "7bit", "8bit", and "binary". |
| $=k | set to be the same as $k, that is, the UUCP node name. |
| $=m | set to the set of domains by which this host is known, initially just $m. |
| $=n | can be set to the set of MIME body types that can never be eight to seven bit encoded. It defaults to "multipart/signed". Message types "message/*" and "multipart/*" are never encoded directly. Multipart messages are always handled recursively. The handling of message/* messages are controlled by class $=s. |
| $=q | A set of Content-Types that will never be encoded as base64 (if they have to be encoded, they will be encoded as quoted-printable). It can have primary types (e.g., "text") or full types (such as "text/plain"). The class is initialized to have "text/plain" only. |
| $=s | contains the set of subtypes of message that can be treated recursively. By default it contains only "rfc822". Other "message/*" types cannot be 8*7 bit encoded. If a message containing eight bit data is sent to a seven bit host, and that message cannot be encoded into seven bits, it will be stripped to 7 bits. |
| $=t | set to the set of trusted users by the T configuration line. If you want to read trusted users from a file use Ft/file/name. |
| $=w | set to be the set of all names this host is known by. This can be used to match local host names. |
sendmail can be compiled to allow a scanf(3S) string on the F line. This lets you do simplistic parsing of text files. For example, to read all the user names in your system /etc/passwd file into a class, use
FL/etc/passwd %[^:]which reads every line up to the first colon.
| Home |
|---|
Programs and interfaces to mailers are defined in this line. The format is:
Mname, {field=value }*where name is the name of the mailer (used internally only) and the "field=name" pairs define attributes of the mailer. Fields are:
Only the first character of the field name is checked.
Path The pathname of the mailer Flags Special flags for this mailer Sender Rewriting set(s) for sender addresses Recipient Rewriting set(s) for recipient addresses Argv An argument vector to pass to this mailer Eol The end-of-line string for this mailer Maxsize The maximum message length to this mailer Linelimit The maximum line length in the message body Directory The working directory for the mailer Userid The default user and group id to run as Nice The nice(2) increment for the mailer Charset The default character set for 8-bit characters Type The MTS type information (used for error messages)
| Home |
|---|
The following flags may be set in the mailer description. Any other flags may be used freely to conditionally assign headers to messages destined for particular mailers. Flags marked with # are not interpreted by the sendmail binary; these are conventionally used to correlate to the flags portion of the H line. Flags marked with ## apply to the mailers for the sender address rather than the usual recipient mailers.
| a | Run Extended SMTP (ESMTP) protocol (defined in RFCs 1651, 1652, and 1653). This flag defaults on if the SMTP greeting message includes the word "ESMTP". |
| A | Look up the user part of the address in the alias database. Normally this is only set for local mailers. |
| b | Force a blank line on the end of a message. This is intended to work around some stupid versions of /bin/mail that require a blank line, but do not provide it themselves. It would not normally be used on network mail. |
| c | Do not include comments in addresses. This should only be used if you have to work around a remote mailer that gets confused by comments. This strips addresses of the form "Phrase <address>" or "address (Comment)" down to just "address". |
| C## | If mail is received from a mailer with this flag set, any addresses in the header that do not have an at sign ("@") after being rewritten by ruleset three will have the "@domain" clause from the sender envelope address tacked on. This allows mail with headers of the form:
From: usera@hosta to be rewritten as:
From: usera@hosta automatically. However, it doesn't really work reliably. |
| d | Do not include angle brackets around route-address syntax addresses. This is useful on mailers that are going to pass addresses to a shell that might interpret angle brackets as I/O redirection. |
| D# | This mailer wants a "Date:" header line. |
| e | This mailer is expensive to connect to, so try to avoid connecting normally; any necessary connection will occur during a queue run. |
| E | Escape lines beginning with "From" in the message with a '>' sign. |
| f | The mailer wants a -f from flag, but only if this is a network forward operation (i.e., the mailer will give an error if the executing user does not have special permissions). |
| F# | This mailer wants a "From:" header line. |
| g | Normally, sendmail sends internally generated email (e.g., error messages) using the null return address as required by RFC 1123. However, some mailers don't accept a null return address. If necessary, you can set the g flag to prevent sendmail from obeying the standards; error messages will be sent as from the MAILER-DAEMON (actually, the value of the $n macro). |
| h | Uppercase should be preserved in host names for this mailer. |
| I | This mailer will be speaking SMTP to another sendmail -- as such it can use special protocol features. This option is not required (i.e., if this option is omitted the transmission will still operate successfully, although perhaps not as efficiently as possible). |
| j | Do User Database rewriting on recipients as well as senders. |
| k | Normally when sendmail connects to a host via SMTP, it checks to make sure that this isn't accidently the same host name as might happen if sendmail is misconfigured or if a long-haul network interface is set in loopback mode. This flag disables the loopback check. It should only be used under very unusual circumstances. |
| K | Currently unimplemented. Reserved for chunking. |
| l | This mailer is local (i.e., final delivery will be performed). |
| L | Limit the line lengths as specified in RFC821. The use of this option is discouraged, and should be replaced by the L= mail declaration. For historic reasons, the L flag also sets the 7 flag. |
| m | This mailer can send to multiple users on the same host in one transaction. When a $u macro occurs in the argv part of the mailer definition, that field will be repeated as necessary for all qualifying users. |
| M# | This mailer wants a "Message-Id:" header line. |
| n | Do not insert a UNIX-style "From" line on the front of the message. |
| o | Always run as the owner of the recipient mailbox. Normally sendmail runs as the sender for locally generated mail or as "daemon" (actually, the user specified in the u option) when deliv ering network mail. The normal behavior is required by most local mailers, which will not allow the envelope sender address to be set unless the mailer is running as daemon. This flag is ignored if the S flag is set. |
| p | Use the route-addr style reverse-path in the SMTP "MAIL FROM:" command rather than just the return address; although this is required in RFC821 section 3.1, many hosts do not process reverse-paths properly. Reverse-paths are officially discouraged by RFC 1123. |
| P# | This mailer wants a "Return-Path:" line. |
| q | When an address that resolves to this mailer is verified (SMTP VRFY command), generate 250 responses instead of 252 responses. This will imply that the address is local. |
| r | Same as f, but sends a -r flag. |
| R | Open SMTP connections from a "secure" port. Secure ports aren't (secure, that is) except on UNIX machines, so it is unclear that this adds anything. |
| s | Strip quote characters (" and \) off of the address before calling the mailer. |
| S | Don't reset the userid before calling the mailer. This would be used in a secure environment where sendmail ran as root. This could be used to avoid forged addresses. If the U= field is also specified, this flag causes the user id to always be set to that user and group (instead of leaving it as root). |
| u | Uppercase should be preserved in user names for this mailer. |
| U | This mailer wants UUCP-style "From" lines with the ugly "remote from <host>" on the end. |
| w | The user must have a valid account on this machine; i.e., getpwnam must succeed. If not, the mail is bounced. This is required to get ".forward" capability. |
| x# | This mailer wants a "Full-Name:" header line. |
| X | This mailer want to use the hidden dot algorithm as specified in RFC821; basically, any line beginning with a dot will have an extra dot prepended (to be stripped at the other end). This ensures that lines in the message containing a dot will not terminate the message prematurely. |
| 0 | Don't look up MX records for hosts sent via SMTP. |
| 3 | Extend the list of characters converted to =XX notation when converting to Quoted-Printable to include those that don't map cleanly between ASCII and EBCDIC. Useful if you have IBM mainframes on site. |
| 5 | If no aliases are found for this address, pass the address through ruleset 5 for possible alternate resolution. This is intended to forward the mail to an alternate delivery spot. |
| 7 | Strip all output to seven bits. This is the default if the L flag is set. Note that clearing this option is not sufficient to get full eight bit data passed through sendmail. If the 7 option is set, this is essentially always set, since the eighth bit was stripped on input. Note that this option will only impact messages that didn't hav e 8*7 bit MIME conversions performed. |
| 8 | If set, it is acceptable to send eight bit data to this mailer; the usual attempt to do 8*7 bit MIME conversions will be bypassed. |
| 9 | If set, do limited 7*8 bit MIME conversions. These conversions are limited to text/plain data. |
| : | Check addresses to see if they begin with ":include:"; if they do, convert them to the "*include*" mailer. |
| | | Check addresses to see if they begin with a '|'; if they do, convert them to the "prog" mailer. |
| / | Check addresses to see if they begin with a '/'; if they do, convert them to the "*file*" mailer. |
| @ | Look up addresses in the user database. |
Configuration files prior to level 6 assume the 'A', 'w', '5', ':', '|', '/', and '@' options on the mailer named "local".
| Home |
|---|
The mailer with the special name "error" can be used to generate a user error. The (optional) host field is an exit status to be returned, and the user field is a message to be printed. The exit status may be numeric or one of the values USAGE, NOUSER, NOHOST, UNAVAILABLE, SOFTWARE, TEMPFAIL, PROTOCOL, or CONFIG to return the corresponding EX_ exit code, or an enhanced error code as described in RFC 1893, Enhanced Mail System Status Codes. For example, the entry:
$#error $@ NOHOST $: Host unknown in this domainon the RHS of a rule will cause the specified error to be generated and the "Host unknown" exit status to be returned if the LHS matches. This mailer is only functional in rulesets 0, 5, or one of the check_* rulesets.
The mailer named "local" must be defined in every configuration file. This is used to deliver local mail, and is treated specially in several ways. Additionally, three other mailers named "prog", "*file*", and "*include*" may be defined to tune the delivery of messages to programs, files, and :include: lists respectively. They default to:
Mprog, P=/bin/sh, F=lsD, A=sh -c $uThe Sender and Recipient rewriting sets may either be a simple ruleset id or may be two ids separated by a slash; if so, the first rewriting set is applied to envelope addresses and the second is applied to headers.
M*file*, P=/dev/null, F=lsDFMPEu, A=FILE
M*include*, P=/dev/null, F=su, A=INCLUDE
The Directory is actually a colon-separated path of directories to try. For example, the definition "D=$z:/" first tries to execute in the recipient's home directory; if that is not available, it tries to execute in the root of the filesystem. This is intended to be used only on the "prog" mailer, since some shells (such as csh) refuse to execute if they cannot read the home directory. Since the queue directory is not normally readable by unprivileged users csh scripts as recipients can fail.
The Userid specifies the default user and group id to run as, overriding the DefaultUser option (q.v.). If the S mailer flag is also specified, this is the user and group to run as in all circumstances. This may be given as user:group to set both the user and group id; either may be an integer or a symbolic name to be looked up in the passwd and group files respectively. If only a symbolic user name is specified, the group id in the passwd file for that user is used as the group id.
The Charset field is used when converting a message to MIME; this is the character set used in the Content-Type: header. If this is not set, the DefaultCharset option is used, and if that is not set, the value "unknown-8bit" is used. WARNING: this field applies to the sender's mailer, not the recipient's mailer. For example, if the envelope sender address lists an address on the local network and the recipient is on an external network, the character set will be set from the Charset= field for the local network mailer, not that of the external network mailer.
The Type= field sets the type information used in MIME error messages as defined by RFC 1894. It is actually three values separated by slashes: the MTA-type (that is, the description of how hosts are named), the address type (the description of e-mail addresses), and the diagnostic type (the description of error diagnostic codes). Each of these must be a registered value or begin with "X-". The default is "dns/rfc822/smtp".
| Home |
|---|
The format of the header lines that sendmail inserts into the message are defined by the H line. The syntax of this line is:
H[?mflags?]hname: htemplateContinuation lines in this spec are reflected directly into the outgoing message. The htemplate is macro expanded before insertion into the message. If the mflags (surrounded by question marks) are specified, at least one of the specified flags must be stated in the mailer definition for this header to be automatically output. If one of these headers is in the input it is reflected to the output regardless of these flags.
Some headers have special semantics that will be described later.
There are a number of global options that can be set from a configuration file. Options are represented by full words; some are also representable as single characters for backward compatibility. The syntax of this line is:
O option=valueThis sets option option to be value. Note that there must be a space between the letter 'O' and the name of the option. An older version is:
Oo valuewhere the option o is a single character. Depending on the option, value may be a string, an integer, a boolean (with legal values "t", "T", "f", or "F"; the default is TRUE), or a time interval.
| Home |
|---|
The options supported (with the old, one character names in brackets) are:
| Home |
|---|
The Address mask may be a numeric address in dot notation or a network name.
Port Name/number of listening port (defaults to "smtp") Addr Address mask (defaults INADDR_ANY) Family Address family (defaults to INET) Listen Size of listen queue (defaults to 5) SndBufSize Size of TCP send buffer RcvBufSize Size of TCP receive buffer
Defaults to "b" if no option is specified, "i" if it is specified but given no argument (i.e., "Od" is equivalent to "Odi"). The -v command line flag sets this to i.
i Deliver interactively (synchronously) b Deliver in background (asynchronously) q Just queue the message (deliver during queue run) d Defer delivery and all map lookups (deliver during queue run)
| Home |
|---|
<@known1,@known2,@known3:user@unknown>sendmail will strip off the "@known1,@known2" in order to make the route as direct as possible. However, if the R option is set, this will be disabled, and the mail will be sent to the first address in the route, even if later addresses are known. This may be useful if you are caught behind a firewall.
In all cases properly declared 8BITMIME data will be converted to 7BIT as needed.
s Reject undeclared 8-bit data ("strict") m Convert undeclared 8-bit data to MIME ("mime") p Pass undeclared 8-bit data ("pass")
| Home |
|---|
p Print error messages (default) q No messages, just give exit status m Mail back errors w Write back errors (mail if user not logged in) e Mail back errors and give zero exit stat always
| Home |
|---|
| Home |
|---|
| Home |
|---|
The "goaway" pseudo-flag sets all flags except "restrictmailq" and "restrictqrun". If mailq is restricted, only people in the same group as the queue directory can print the queue. If queue runs are restricted, only root and the owner of the queue directory can run the queue. Authentication Warnings add warnings about various conditions that may indicate attempts to spoof the mail system, such as using a non-standard queue directory.
public Allow open access needmailhelo Insist on HELO or EHLO command before MAIL needexpnhelo Insist on HELO or EHLO command before EXPN noexpn Disallow EXPN entirely needvrfyhelo Insist on HELO or EHLO command before VRFY novrfy Disallow VRFY entirely restrictmailq Restrict mailq command restrictqrun Restrict -q command line flag noreceipts Don't return success DSNs goaway Disallow essentially all SMTP status queries authwarnings Put X-Authentication-Warning: headers in messages
| Home |
|---|
This avoids a certain class of security problems. However, this means that all ".forward" and ":include:" files must be readable by the indicated user, and on systems that don't support the saved uid bit properly, all files to be written must be writeable by user and all programs will be executed by user. It is also incompatible with the SafeFileEnvironment option. In other words, it may not actually add much to security on an average system, and may in fact detract from security (because other file permissions must be loosened). However, it should be useful on firewalls and other places where users don't have accounts and the aliases file is well constrained.