Zen and the Art of Internet | Page 7

mail at your site.
A person sending the author mail would probably do something like this:
% mail [email protected] Subject: print job's stuck
I typed `print babe.gif' and it didn't work! Why??
The next time the author checked his mail, he would see it listed in his mailbox as:
% mail "/usr/spool/mail/brendan": 1 messages 1 new 1 unread U 1 [email protected]
Tue May 5 20:36 29/956 print job's stuck ?
which gives information on the sender of the email, when it was sent, and the subject of
the message. He would probably use the reply command of Unix mail to send this
response:
? r To: joeuser@@foo.widener.edu Subject: Re: print job's stuck
You shouldn't print binary files like GIFs to a printer!
Brendan
Try sending yourself mail a few times, to get used to your system's mailer. It'll save a lot
of wasted aspirin for both you and your system administrator.
Anatomy of a Mail Header
An electronic mail message has a specific structure to it that's common across every type
of computer system. {The standard is written down in RFC-822. See also RFCs for more
info on how to get copies of the various RFCs.} A sample would be:
>From [email protected] Sat May 25 17:06:01 1991 Received: from hq.mil by house.gov
with SMTP id AA21901 (4.1/SMI for [email protected]); Sat, 25 May 91 17:05:56 -0400
Date: Sat, 25 May 91 17:05:56 -0400 From: The President Message-Id:
<[email protected]> To: [email protected] Subject: Meeting
Hi Dan .. we have a meeting at 9:30 a.m. with the Joint Chiefs. Please don't oversleep this
time.
The first line, with From and the two lines for Received: are usually not very interesting.
They give the ``real'' address that the mail is coming from (as opposed to the address you
should reply to, which may look much different), and what places the mail went through
to get to you. Over the Internet, there is always at least one Received: header and usually
no more than four or five. When a message is sent using UUCP, one Received: header is
added for each system that the mail passes through. This can often result in more than a

dozen Received: headers. While they help with dissecting problems in mail delivery,
odds are the average user will never want to see them. Most mail programs will filter out
this kind of ``cruft'' in a header.
The Date: header contains the date and time the message was sent. Likewise, the ``good''
address (as opposed to ``real'' address) is laid out in the From: header. Sometimes it won't
include the full name of the person (in this case The President), and may look different,
but it should always contain an email address of some form.
The Message-ID: of a message is intended mainly for tracing mail routing, and is rarely
of interest to normal users. Every Message-ID: is guaranteed to be unique.
To: lists the email address (or addresses) of the recipients of the message. There may be a
Cc: header, listing additional addresses. Finally, a brief subject for the message goes in
the Subject: header.
The exact order of a message's headers may vary from system to system, but it will
always include these fundamental headers that are vital to proper delivery.
Bounced Mail
When an email address is incorrect in some way (the system's name is wrong, the domain
doesn't exist, whatever), the mail system will bounce the message back to the sender,
much the same way that the Postal Service does when you send a letter to a bad street
address. The message will include the reason for the bounce; a common error is
addressing mail to an account name that doesn't exist. For example, writing to Lisa
Simpson at Widener University's Computer Science department will fail, because she
doesn't have an account. {Though if she asked, we'd certainly give her one.}
From: Mail Delivery Subsystem Date: Sat, 25 May 91 16:45:14
-0400 To: [email protected] Cc: [email protected] Subject: Returned mail: User
unknown
----- Transcript of session follows ----- While talking to cs.widener.edu: >>> RCPT
To: <<< 550 ... User unknown
550 lsimpson... User unknown
As you can see, a carbon copy of the message (the Cc: header entry) was sent to the
postmaster of Widener's CS department. The Postmaster is responsible for maintaining a
reliable mail system on his system. Usually postmasters at sites will attempt to aid you in
getting your mail where it's supposed to go. If a typing error was made, then try
re-sending the message. If you're sure that the address is correct, contact the postmaster
of the site directly and ask him how to properly address it.
The message also includes the text of the mail, so you don't have to retype everything you
wrote.
----- Unsent message follows ----- Received: by cs.widener.edu