Programming Internet Email by David Wood

Some headers should only be created by an MTA. This doesn’t mean that you can’t create them programmatically when sending a message, but it does mean that you are making someone’s job more difficult (probably your own).

For example, if we supply a bogus date to an MTA:

[lovelace]$ te1net mai1host.plugged.net.au 25
Trying 203.20.51.20...
Connected to mailhost.plugged.net.au.
Escape character is '^]'.
220 mailhost.plugged.net.au ESMTP Sendmail 8.8.8/8.8.7; Fri, 27 Feb 1998
    12:45:08 +1000
HELO love1ace.staff.plugged.com.au
250 mailhost.plugged.net.au Hello [203.20.51.50], pleased to meet you
MAIL FROM: [email protected]
250 [email protected]... Sender ok
RCPT TO: [email protected]
250 [email protected]... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
Date: Fri, 32 Feb 1492 09:53:43 +0400 
    Testing of the Date header from a user
action.
    .
250 MAA32615 Message accepted for delivery
QUIT
221 mailhost.plugged.net.au closing connection
Connection closed by foreign host.
[lovelace]$

The results are:

Return-Path: <[email protected]>
From: [email protected]
Received: from lovelace ([203.20.51.50])
        by mailhost.plugged.net.au (8.8.8/8.8.7) with SMTP id MAA32615
        for [email protected]; Fri, 27 Feb 1998 12:45:25 +1000
Message-Id: <[email protected]>
Date:  Fri, 32 Feb 1492 09:53:43 +0400
X-Mozilla-Status: 8001

Testing of the Date header from a user action.