The Network Connection
This column is a continuing feature of Benchmarks intended to
present news and information on various aspects of wide area networks.
Know Your Mail Header
If you have received Internet mail, you may have noticed all that
stuff at the top which we technical types like to call the mail header.
The part you usually notice may be the Date:, To:, From: and Subject:
fields, but some other parts may be useful on occasion as well. The
basic rules for constructing mail headers are known by most E-mail
programs and are described in a document known as RFC 822 (RFC stands
for Request for Comment and RFCs are numbered sequentially as they are
published on the Internet).It is the standardization of these header
fields that allow differing computer systems to easily transmit mail
across the Internet.
By examining a typical message header, we can gain further
understanding of the different fields and perhaps gain additional
insight for interpreting messages which have delivery problems or a less
than clear origin.
What follows below is a typical Internet mail header. It was part of
a message sent to me by one of UNT s former staffers. At first glance,
it might seem quite a jumble, but by analyzing different sections, it s
interpretation becomes quite a bit easier.
Received: from UNTVM1 by VM.ACS.UNT.EDU (Mailer R2.07) with BSMTP id 3111; Wed, 21 Dec 94 13:30:17 CST
Received: from is.rice.edu by VM.ACS.UNT.EDU (IBM VM SMTP V2R1) with TCP;
Wed, 21 Dec 94 13:29:46 CST
Received: from brigadoon.rice.edu by is.rice.edu (AA28265); Wed, 21 Dec 94 13:28:48 CST
Message-Id: 11928.AA28265@is.rice.edu
X-Sender: kevinm@is.rice.edu
X-Mailer: Windows Eudora Version 1.4.3
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Date: Wed, 21 Dec 1994 14:30:59 -0600
To: ac12@vm.acs.unt.edu
From: kevinm@is.rice.edu (Kevin Mullet)
Subject: Kermit snippet
It may help to examine this header in reverse. From the bottom up, the first part should be familiar:
Date: Wed, 21 Dec 1994 14:30:59 -0600
To: ac12@vm.acs.unt.edu
From: kevinm@is.rice.edu (Kevin Mullet)
Subject: Kermit snippet
The last section, shown above, has the date, sender s address,
recipient s address, and the message subject. This is the easy part.
The rest might need more explanation.
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
The above two lines indicate that the mail program used to send the
message supports the MIME protocol (allowing multimedia attachments).
The first line shows the MIME version used and the second line shows the
nature of any attachments, in this case simply a text-only message.
Working our way up the header, we find the following two lines:
X-Sender: kevinm@is.rice.edu
X-Mailer: Windows Eudora Version 1.4.3
Any field starting with an X indicates an extension to the normal
header fields. Extensions can be inserted by the mail program (and
sometimes by the mail program user) and provide information which may
not be part of a standard header or which might be useful to the
receiving mail program when processing an incoming message. These two
lines confirm the sender of the message and indicate what mail program
was used to send it.
Every Internet message is given an arbitrarily assigned message
identification and this is shown in the following line:
Message-Id: 11928.AA28265@is.rice.edu
You can see that the message ID above is partly formed from message
date (941221 is derived from Dec. 12, 94) and ends with the originating
node.
The first three lines of the header show the path your message took
to reach you:
Received: from UNTVM1 by VM.ACS.UNT.EDU (Mailer R2.07) with BSMTP id 3111; Wed, 21 Dec 94 13:30:17 CST
Received: from is.rice.edu by VM.ACS.UNT.EDU (IBM VM SMTP V2R1) with TCP;
Wed, 21 Dec 94 13:29:46 CST
Received: from brigadoon.rice.edu by is.rice.edu (AA28265); Wed, 21 Dec 94
13:28:48 CST
There are actually three header fields defined here, each beginning
with the Received: header element. These are listed in the reverse
order of actual transmission. Examining these one at a time from the
bottom up we can see the path that this message traversed to reach me.
Received: from brigadoon.rice.edu by is.rice.edu (AA28265); Wed, 21 Dec 94
13:28:48 CST
The above line shows that the message started from a machine named
brigadoon.rice .edu and was transmitted to is.rice.edu . Moving up
our header example we see:
Received: from is.rice.edu by VM.ACS.UNT.EDU (IBM VM SMTP V2R1) with TCP;
Wed, 21 Dec 94 13:29:46 CST
The computer, is.rice.edu transmitted the message to vm.acs.unt.edu
(UNT s academic mainframe). The Received field also shows what software
facility handled the transaction. In the parentheses above, we can see
that this was received by the IBM VM SMTP software (the Internet mail
program).
Finally, the message gets to me:
Received: from UNTVM1 by VM.ACS.UNT.EDU (Mailer R2.07) with BSMTP id 3111; Wed,
21 Dec 94 13:30:17 CST
VM s Mailer program is the software that actually delivered the
message to my CMS User-ID. You will also notice that each Received:
field shows the time that the mail transaction (the passing of the
message from one computer system to another) occurred. If you think your
mail is delayed in arriving, you can check the Received fields to see if
it is getting stuck at some point along the way.
That s the end of Headers 101 and hopefully, this has been a
revelation of some of that Internet mystery. You can find out more by
reading RFC 822 or any number of Internet books that are available
commercially. I can t reveal all the Internet mysteries here, however.
After all, you have to hold back some of those mysteries if you are
going to be considered a guru.
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