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 <MAILER-DAEMON>
Date: Sat, 25 May 91 16:45:14 -0400
To: mg@gracie.com
Cc: Postmaster@cs.widener.edu
Subject: Returned mail: User unknown
——- Transcript of session follows ——- While talking to cs.widener.edu: >>> RCPT To:<lsimpson@cs.widener.edu> <<< 550 <lsimpson@cs.widener.edu>… User unknown 550 lsimpson… User unknown