sendmail.cf(4) Kernel Interfaces Manual sendmail.cf(4)
NAME
sendmail.cf - Contains the sendmail configuration file data
SYNOPSIS
/var/adm/sendmail/sendmail.cf
DESCRIPTION
The sendmail.cf file contains configuration information for the sendmail daemon. For further information on sendmail, see the sendmail(8)
reference page, the sendmail book by O'Reilly & Associates, or the Sendmail Installation and Operation Guide. The latter is available on
the Documentation CD-ROM.
The sendmail.cf configuration file consists of a series of control lines, each of which begins with a single character that defines how the
rest of the line is used. Lines beginning with a space or a tab are continuation lines. Blank lines and lines beginning with a # (number
sign) are comments. The control line can be used for the following functions: Defining macros and classes for use within the configuration
file Defining message precedence for mail delivery Defining administrative IDs to override the sender's address Defining message headings
Defining the mail daemon to use Defining the syntax version used within the configuration file Defining rules and rule sets Setting options
used by the sendmail command
Defining Syntax Version (V Control Line)
To specify the syntax version used by the sendmail.cf configuration file, use Vn[vendorcode], where n is an integer specifying the syntax
version. If n is omitted, the original level 0 is assumed. An optional vendor code can follow the level. The files supplied by Compaq use
"V2/DIGITAL" to specify the syntax version.
Tru64 UNIX provides tools to help you create a reasonable sendmail.cf file. See the mailconfig(8) and the mailsetup(8) reference pages for
further information.
Defining Rules and Rule Sets (R Control Line and S Control Line)
Most of the sendmail.cf file consists of rules (R Control lines) and rule sets. A rule set is a group of rules, prefixed by an S control
line. For example, S3 is rule set 3, while S99 is referred to as rule set 99.
While a rule set must start with an S control line, there is no obvious "end-of-ruleset" marker. All rules following an S control line are
considered to be part of that rule until either a new S control line, or the end of the file are encountered.
Defining Macros and Classes (D Control Line and C Control Line)
Macros and classes in the sendmail.cf configuration file are interpreted by the sendmail daemon. A macro is a symbol that represents a
value or string, for example, or an Internet address. A macro is defined by a D control line in the sendmail.cf file. Macros are not
expanded until the sendmail daemon loads the rule sets when it starts up. The sendmail.cf file contains system-defined macros and required
macros that you must define.
A class is a symbol that represents a set of one or more words, for example, or a filename. Classes are used in pattern matching when the
sendmail daemon is parsing addresses. You can create a class using a list or you can create a class using a file.
The following letters introduce configuration file control lines that define macros and classes to set up the sendmail daemon: Defines a
macro and assigns a value to it. If a second DMacroValue defines the same macro, the second definition replaces the first definition. The
macro can be a single character or a word in braces {}. For single character macros, you must use only uppercase letters. Similarly, for
longer macros, the first character must be an uppercase letter. Single character macros that are lower case letters or special symbols are
reserved for use by sendmail, as are words beginning with a lower case letter or punctuation character. Defines Class to be a class and
assigns a word or group of words (String) to it. If a second CClass String defines the same symbol, the String from the second definition
is added to the String from the first definition. No words are deleted from the class definition. Class specifiers may be any of the
uppercase letters from the ASCII character set. Lowercase letters and special characters are reserved for system use. Defines symbol
Class to be a class and assigns a word or group of words listed in a separate file to the symbol. You can specify an optional scanf format
specifier. Class specifiers may be any of the uppercase letters from the ASCII character set. Lowercase letters and special characters
are reserved for system use.
To use a macro or class in a control line, put a $ (dollar sign) before its name. For example, if the name of the macro is x, use $x when
using that macro in a control line. Without the preceding $, the daemon interprets x as only the letter "x". The format for specifying
conditional expressions is as follows: $?Macro Text1 $| Text2 $.
In this format, the symbols have the following meaning: If. The macro being tested. The pattern to be used if $x is defined. Else.
(This symbol is not required.) The pattern to be used if $Macro is not defined. Specifies the end of the conditional expression.
Do not use any of the characters defined as tokens (by the required macro o) when defining a word in a class. The sendmail daemon may not
be able to read the definition correctly.
Defining Message Precedence (P Control Line)
The sendmail.cf configuration file also contains lines to define mail-queue precedence for messages that contain a Precedence: field. Nor-
mally, you do not need to change the values in the default sendmail.cf configuration file.
The name defined and the numerical value assigned are based on the needs of the network. Higher numbers have higher priority; numbers less
than 0 (zero) indicate that error messages will not be returned to the sender of these messages. The precedence value is 0 (zero) for any
precedence name not defined in this file. For example, the configuration file may contain the following entries: Pfirst-class=0 Pspecial-
delivery=100 Pbulk=-60 Pjunk=-100
These entries set special-delivery as the highest priority message and junk as the lowest priority.
Defining Administrative IDs (T Control Line)
Administrative IDs can override the sender address using the -f flag to the sendmail command. The sendmail.cf configuration file defines
these IDs with the T control line. For example, the configuration file may contain the following entries: Troot Tdaemon Tuucp
These entries define IDs root, daemon, and uucp as administrative IDs for the sendmail command. Alternatively, these IDs could have been
defined using only one T control line: Troot daemon uucp network
Defining Message Headings (H Control Line)
H control lines define the format of Header lines. If the format of a header line is defined by an H control line, sendmail will reformat
the header according to this format.
The sendmail command allows the user to configure whether a header is optional or not depending on the mailer (M control lines) selected to
handle this message. If the selected mailer has the MailerFlag defined in its F= section, then the header is added. For instance, most
mailers have the F=D flag set; this enables the Date: header to be included in the message.
The format of the H control line is as follows: H[?MailerFlags?]FieldName: format
In this format, the variable parameters have the following meaning: This field is optional. If you supply it, surround it with ? (question
marks). This field contains mailer flags that determine whether this H line is used. If the mailer being used requires the information
specified by the mailer flag, then this H control line is included when formatting the heading. Otherwise, this H control line is ignored.
This field contains the text that is displayed as the name of the field in the heading information. The actual text used is a matter of
choice. Some typical field names include From:, To:, and Rcvd From:. This field defines the information that is displayed following the
field name. It usually uses a sendmail macro to specify the information.
The sendmail command does not do any special processing for the header mailer flags; their use is purely by convention. See the section on
Specifying Mailer Flags for more detail.
The following is a list of parts that the sendmail daemon expects mail to have. Note that these parts must appear in the same order as
listed here. An operating system From line (defined by the five characters: F, r, o, m, and space) Mail header lines that begin with a
keyword followed by a colon, such as From: or To: An empty line The body of the message
The sendmail daemon detects the operating system From line by checking the first five characters of the first line. After that, header
lines are processed. When it detects a line that does not begin with a keyword followed by a colon, it ends header line processing. If an
empty line occurs at that point, it is ignored.
Mailer flags or the mailer itself determine if an operating system From: line is generated. Other header lines are present (or not)
depending on those defined in the sendmail configuration file, those specified by mailer flags, and those present in incoming mail.
Note that the binmail daemon generates a From: line on all local deliveries. The sendmail mailer flags do not allow you to alter this.
The following example lines are from a typical sendmail.cf file: H?P?Return-Path: <$g>
This line defines a field called Return-Path: that displays the contents of the $g macro (sender address relative to the receiver). The
?P? portion indicates that this line is only used if the mailer uses the P flag (the mailer requires a Return-Path line). HReceived:
$?sfrom $s $.by $j ($v/$Z)
id $i; $b
This line defines a field called Received. This field displays the following information: If an s macro is defined (sender's hostname),
displays the text from followed by the content of the $s macro. Displays the text by followed by the content of the $j macro (official
name for this site). Displays the version of the sendmail daemon ($v) and the version of the sendmail.cf file ($Z) set off by parentheses
and separated by a slash. Displays the text id followed by the content of the $i macro (mail-queue ID of the message) and a ; (semicolon).
Displays the current date.
Defining a Mailer (M Control Line)
A mailer is a daemon that delivers mail either locally or over some type of network to another system. Use control lines that begin with
the letter M to define the characteristics of a mailer daemon that interfaces with sendmail.
Note that defining a mail daemon entry (mailer) in the sendmail.cf configuration file does not ensure that it will be used. You must also
define rewrite rules to ensure the address format resolves to that mailer.
The format of a mailer definition control line is as follows: M=MailerName, P=Path, F=Flags, S=Integers,E=EndOfLine, A=String, M=Limit
The following paragraphs and examples describe the parameters for the mailer definition.
Specifying a Mailer Name (MMailerName)
Each mailer must have an internal name. The name can be any string that you choose, except that the names local and prog are reserved for
the mailers for local delivery and delivery to daemons. You must provide definitions for these two mailers in the sendmail.cf configura-
tion file if they are not already there (the default configuration file contains these definitions). To define the mailer name, put the
name immediately after the M in the mailer-definition control line: MMailerName
For example, the following segment introduces the definition line for a mailer called lan: Mlan
Defining the Path to the Mailer Daemon (P=Path)
Specify the location of the mailer daemon with the P field in the mailer definition. This field has the format: P=Path
The Path defines the full pathname of the mailer daemon on the local system. If the mailer daemon is the sendmail daemon version of Simple
Mail Transfer Protocol (SMTP) (daemon), use the string [IPC] as the path. For example, the following two mailer-definition fragments
define a local mailer at /usr/bin/mail and another mailer that is the sendmail daemon implementation of SMTP: Mlocal, P=/usr/bin/mail,
Mlan, P=[IPC],
Specifying Mailer Flags (F=Flags)
Mailer flags provide further information to the sendmail daemon about the mailer daemon being described. Specify mailer flags with the F
field in the mailer-definition. This field has the format: F=Flags
This field defines the meaning for the flags that the sendmail daemon recognizes. For example, the following mailer-definition fragment
uses the -rlsm flags to indicate that the mailer requires a -r flag, delivers locally, needs quotation marks stripped from addresses, and
can deliver to more than one user at a time: Mlocal, P=/usr/bin/mail, F=rlsm,
Flags available for the F=Flags field are as follows: If this flag is set, this mailer inspects the address of any incoming mail that it
processes for the presence of an @ (at sign). If it finds an @, it saves the @ and the remainder of the address to be used when rewriting
addresses in header lines in the message (when mail is forwarded to any mailer).
The receiving mailer adds the saved portion of the address to any address that does not contain an @, after the address has been
processed by rule set 3 (this processing does not depend upon a mailer flag; it always occurs). Do not use this flag for general
operation, since it does not interpret complex, route-based addresses properly. The mailer defined in this mailer-definition con-
trol line needs a Date: or Resent-Date: header line. The mailer defined in this mailer-definition control line is expensive to con-
nect to. If the C configuration option is set, mail for this mailer is always placed in the queue. This flag causes the mailer in
the definition control line to allow lines beginning with the exact six characters >, F, r, o, m, and space to appear in the text
of a message. Normally From: lines are treated as header lines. The E flag allows operating system From: lines (or any other text
lines beginning with those six characters) to appear in the body of the message without being interpreted as the start of a new mes-
sage. The mailer in the mailer-definition control line needs a -f flag. The flag is inserted into the call for the mailer followed
by the expansion of the $g macro (sender's address relative to the receiver). The mailer in the mailer-definition control line
needs a From: or Resent-From: header line. This header is optional depending on the mailer (M control lines) selected to handle this
message. Preserves uppercase letters in hostnames for the mailer in the mailer-definition control line. The mailer in the mailer-
definition control line uses Simple Mail Transfer Protocol (SMTP) to communicate with another SMTP server that is part of the send-
mail daemon. When communicating with another sendmail daemon, the mailer can use features that are not part of the standard SMTP
protocol. This option is not required, but causes the transmission to operate more efficiently than without the option. The mailer
in the mailer-definition control line is local; final delivery will be performed. The L flag enforces SMTP line lengths. The
mailer in the mailer-definition control line can be sent to multiple users on the same host in one transaction. The $u macro con-
tains the recipient's username. When a $u macro occurs in the String part of the mailer-definition, (for example A=mail -r $g -d
$u) and the m flag is set, $u is expanded to become a list of all the recipients. The mailer in the mailer-definition control line
needs a Message-Id header. This header is optional depending on the mailer (M control lines) selected to handle this message. The
mailer in the mailer-definition control line needs a Return-Path: header line. This header is optional depending on the mailer (M
control lines) selected to handle this message. The mailer in the mailer-definition control line needs a Full-name: header. This
header is optional depending on the mailer (M control lines) selected to handle this message. For versions prior to Version 8, this
flag also enables the MULT option required by the mail11v3 program to handle multiple recipients.
Define Sender Rewriting Rules (S=Envelope/Header)
Define Recipient Rewriting Rules (R=Envelope/Header)
After a mailer has been selected by the S0 ruleset, sendmail performs additional processing on the addresses. Sender addresses are pro-
cessed by the rule(s) specified by the S= section, while recipient addresses are processed by the rule(s) specified by the R= section.
The sendmail program allows you to specify either a single rule (for example, S=14), or split rewriting rules. (For example, S=14/24). If
split rules are specified, envelope addresses are processed by the first rule (for example, 14), while header addresses are processed by
the later rule (for example, 24).
Configuration File Revision Level Option (DZNumber)
The configuration file revision level macro, Z, helps you track changes that you make to the sendmail configuration file. Each time that
you make a change to the sendmail configuration file, you should also change the value of this macro. Choose any format for the number
that you define. For example, if the sendmail configuration file is at level 3.1, the following entry appears in the sendmail configura-
tion file: DZ3.1
A text string can also be used for this macro: DZversion_one
Defining a Map (K Key File Declaration)
You can define a special map function with the following line: Kmapname mapclass arguments The fields in the definition have the following
purposes: Indicates the handle of this map, which is referenced in the rewriting rules Indicates the type of the map (for example, dbm,
ldapx, text, etc. These are compiled into sendmail.) Contains one or more arguments depending on the type of the map (for example, a sin-
gle argument naming the file that contains the map)
Once defined, map functions are called with the following syntax: $(mapname key $@ arguments $: default $) The $@ arguments and $: default
fields are optional, and the $@ arguments field can appear more than once.
Sendmail passes the specified key and arguments to the appropriate mapping function. If the function returns a value, the value replaces
the input. If the function does not return a value, and a default is specified, the default replaces the input. Otherwise, the input
remains unchanged.
For example, the following rule looks up the UUCP name in a (user-defined) UUCP map: R$-!$+ $: $(uucp $1 $@ $2 $: %1 @ %0 .UUCP $)
If the name is not found, sendmail turns it into the following: research %1@%0.ATT.COM
RELATED INFORMATION
Commands: mailconfig(8), mailsetup(8), mail_manual_setup(7), sendmail.m4(8), sendmail(8) delim off
sendmail.cf(4)