The
sendmail
program
contains an internal list of header
name
s 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.
Except for
Received:
(see
Section 35.10.25
), none is added to any mail message
that already has that particular header present.
The
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
F=P
flag
present. Similarly, the
Date:
relies on
F=D
, the
From:
relies on
F=F
, the
Full-Name:
relies
on
F=x
, and the
Message=Id:
relies on
F=M
.
Of those shown, only the seven indicated are truly mandatory
and must be declared in
every
configuration file. The others are highly recommended.
Certain header
name
s are assumed by
sendmail
to
contain information about the various possible senders of a mail
message. They are listed in
Table 35.3
in descending order of significance. Addresses with the H_FROM flag
(see
Section 35.5.9
) are rewritten as sender addresses.
Table 35.3: Sender Headers (Most to Least Significant)
Header |
|
Flags |
Defined by |
Resent-Sender:
|
Section 35.7, "Forwarding with Resent-Headers"
|
H_FROM, H_RESENT |
RFC822 |
Resent-From:
|
Section 35.10.14, From:
|
H_FROM, H_RESENT |
RFC822 |
Resent-Reply-To:
|
Section 35.7
|
H_FROM, H_RESENT |
RFC822 |
Sender:
|
Section 35.10.30, Sender:
|
H_FROM |
RFC822 |
From:
|
Section 35.10.14
|
H_FROM |
RFC822 |
Apparently-From:
|
Section 35.10.1, Apparently-From:
|
n/a |
Smail 3.0 |
Reply-To:
|
Section 35.10.27, Reply-To:
|
H_FROM |
RFC822 |
Full-Name:
|
Section 35.10.15, Full-Name:
|
H_ACHECK |
obsolete |
Return-Receipt-To:
|
Section 35.10.29, Return-Receipt-To:
|
H_FROM |
obsolete |
Errors-To:
|
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
the
UseErrorsTo
(
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
.
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
.
Note that the
Precedence:
and
Posted-Date:
(below) headers
are hard-coded into
sendmail
rather than being declared in
conf.c
.
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
.
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
Return-Path:
,
should be declared in the configuration file. The others are usually
inserted by MUAs.
Table 35.7
lists these other RFC822 headers.
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
.
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