The sendmail program
contains an internal list of header
names that are
organized conceptually into categories.
The names and categories are defined in conf.c (see Section 35.5, "Header Behavior in conf.c").
Each category is defined by one or more
H_ flags in that file,
the names of which are listed under the Flags column
of all the tables that follow.
Every sendmail.cf file should have a minimal complement of header definitions. Below we present a recommendation. Don't use this as is. The details are not generic to all versions of sendmail, nor are they appropriate for all sites.
H?P?Return-Path: $g HReceived: $?sfrom $s $.by $j ($v/$V) id $i; $b mandatory H?D?Date: $a mandatory H?F?From: $q mandatory H?x?Full-Name: $x H?M?Message-Id: <$t.$i@$j> mandatory H?D?Resent-Date: $a mandatory H?F?Resent-From: $q mandatory H?M?Resent-Message-Id: <$t.$i@$j> mandatory
Each of these is described individually at the end of this chapter.
Received: (see Section 35.10.25), none is added to any mail message
that already has that particular header present.
Return-Path: header (see Section 35.10.28)
is added only if it is not already present and
if the delivery agent for the recipient has the
present. Similarly, the
Date: relies on
From: relies on
F=x, and the
Message=Id: relies on
Of those shown, only the seven indicated are truly mandatory and must be declared in every configuration file. The others are highly recommended.
names are assumed by sendmail to
contain information about the various possible senders of a mail
message. They are listed in
in descending order of significance. Addresses with the H_FROM flag
(see Section 35.5.9) are rewritten as sender addresses.
|Section 35.7, "Forwarding with Resent-Headers"||H_FROM, H_RESENT||RFC822|
|Section 35.10.14, From:||H_FROM, H_RESENT||RFC822|
|Section 35.7||H_FROM, H_RESENT||RFC822|
|Section 35.10.30, Sender:||H_FROM||RFC822|
|Section 35.10.1, Apparently-From:||n/a||Smail 3.0|
|Section 35.10.27, Reply-To:||H_FROM||RFC822|
|Section 35.10.15, Full-Name:||H_ACHECK||obsolete|
|Section 35.10.29, Return-Receipt-To:||H_FROM||obsolete|
|Section 35.10.13, Errors-To:||H_FROM, H_ERRSTO||sendmail|
When returning bounced mail, sendmail
always uses the envelope sender's address.
If the special header
Errors-To: appears in the message,
a copy of the bounced mail is also sent to the address in that header.
This is hard-coded
into all but SunOS and V8 sendmail, which use
the H_ERRSTO header flag (see Section 35.5.11) instead.
V8 also requires that
l) option (see Section 34.8.74)
be set to true for the
Errors-To: header to be honored.
Recipient headers are those from which one or more recipients
can be parsed.
Addresses in headers with the H_RCPT flag (see Section 35.5.2) are
rewritten as recipient addresses.
When they are invoked with the
-t command-line switch, sendmail gathers a
list of recipients from all the headers marked with an H_RCPT
flag and delivers a copy of the message to each.
The list of recipient headers used by sendmail is shown in Table 35.4.
|Section 35.10.33, To:||H_RCPT||RFC822|
|Section 35.7||H_RCPT, H_RESENT||RFC822|
|Section 35.10.5, Cc:||H_RCPT||RFC822|
|Section 35.7||H_RCPT, H_RESENT||RFC822|
|Section 35.10.4||H_RCPT, H_ACHECK||RFC822|
|Section 35.7||H_RCPT, H_ACHECK, H_RESENT||RFC822|
|Section 35.10.2, Apparently-To:||H_RCPT||Obsolete|
Some headers serve to uniquely identify a mail message. Others affect the way sendmail processes a mail message. The complete list of all such identification and control headers is shown in Table 35.5.
|Section 35.10.20, Message:||H_EOH||Obsolete|
|Section 35.10.32, Text:||H_EOH||Obsolete|
|Section 35.8, "Precedence"||n/a||All sendmails|
|Section 35.10.24, Priority:||n/a||V8.7 and above|
Note that the
Posted-Date: (below) headers
are hard-coded into sendmail rather than being declared in
Date headers are used to document the date and time that the mail message was sent or forwarded. Trace headers (those with an H_TRACE header flag; see Section 35.5.8) are used to determine the hop count of a mail message and to document the message's travel from machine to machine. The list date and trace headers is shown in Table 35.6.
|Section 35.10.10, Date:||n/a||RFC822|
|Section 35.10.22, Posted-Date:||n/a||Obsolete|
|Section 35.10.25||H_TRACE, H_FORCE||RFC822|
|Section 35.10.34, Via:||H_TRACE, H_FORCE||Obsolete|
|Section 35.10.18, Mail-From:||H_TRACE, H_FORCE||Obsolete|
|Section 35.10.35, X-Authentication-Warning:||n/a||V8 sendmail|
|Section 35.10.36, X400-Received:||H_TRACE||IDA and V8 only|
Other headers that you will see in mail messages are defined by
the RFC822 standard but are not otherwise internally defined
by sendmail. A few of them, such as
should be declared in the configuration file. The others are usually
inserted by MUAs.
lists these other RFC822 headers.
|Section 35.10.16, In-Reply-To:||n/a||RFC822|
|Section 35.10.26, References:||n/a||RFC822|
|Section 35.10.17, Keywords:||n/a||RFC822|
|Section 35.10.6, Comments:||H_FORCE||RFC822|
|Section 35.10.12, Encrypted:||n/a||RFC822|
MIME (Multipurpose Internet Mail Extensions) is documented in RFC1521, with additional details in RFC1344, RFC1426, RFC1428, and RFC1437. The sendmail program cares about MIME only when bouncing messages and when determining how to convert the message body between 8 and 7 bits. Those MIME headers for which sendmail contains special knowledge are shown in Table 35.8.
|Section 35.10.21, MIME-Version:||n/a||RFC1521|