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
(Section 25.6). Each category is defined by one or
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. Here 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: (Received:), none is added to any mail message that
already has that particular header present.
Return-Path: header (Return-Path:) 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
From: relies on
Full-Name: relies on
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.