From you@Here.US.EDU Fri Dec 13 08:11:44 1996 Received: (from you@localhost) by Here.US.EDU (8.8.4/8.8.4) id AA04599 for you; Fri, 13 Dec 96 08:11:44 -0700 Date: Fri, 13 Dec 96 08:11:43 From: you@Here.US.EDU (Your Full Name) Message-Id: <9631121611.AA02124@Here.US.EDU> To: you may be something else (see Section 34.8.43, NoRecipientAction)
Notice that most header lines start with a word followed
by a colon. Each word tells what kind of information the rest of
the line contains.
There are many types of header lines that can appear in a mail message.
Some are mandatory, some are optional, and some may appear
many times. Those that appeared in the message that you mailed
to yourself were all mandatory. That's why sendmail added them to
The line starting with the five characters "
(the fifth character is a space) is added by some programs (such as
/bin/mail) but not by others (such as mh).
Received: line is added each time a machine
receives the mail message.
(If there are too many such lines, the mail message will bounce and be
returned to the sender as failed mail.)
The indented line is a continuation of the line above, the
Date: line gives the date and time when the message
was originally sent.
From: line lists the email address and the full
name of the sender.
Message-ID: line is like a serial number in that it
is guaranteed to uniquely identify the mail message.
line shows a list of one or more recipients.
(Multiple recipients would be separated with commas.)
 Depending on how the
NoRecipientActionoption was set, this could be an
Bcc:header, or even a
To:header followed by an "
undisclosed-recipients:;" (see Section 34.8.43).
A complete list of all header lines that are of importance to sendmail is presented in Chapter 35, Headers. The important concept here is that the header precedes, and is separate from, the body in all mail messages.