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Introduction to Email Structure of a mail message

A mail message consists of a header, which contains information about who the message was sent from, the recipient(s) and the route. Many of the header fields are not shown by default, but most programs used to read email will allow full headers to be displayed. This is then followed by the body of the message which contains whatever the sender wishes. lf the mail message is a formal one, it is customary although not obligatory to finish with your name, return address and other useful information as a signature. For example:

Netscape have released a new version of Netscape Communicator (4.75) which is not subject to the Java vulnerability announced preciously on this list.
If you use a vulnerable version of Netscape (version 4.0 - 4.74) it is
recommended that you upgrade.

Chris Bayliss
Information Services

The header consists of lines beginning with a keyword followed by a colon (:), followed by information on each line. A brief explanation of each field of the header is given below. This header contains most of the common fields.
Received: These lines indicate the route that the email has taken and which systems have handled it and the times that it was handled.

Date: The date and time at which the message was sent including time zone.

From: The sender. The part in angle brackets is a real electronic mail address. This field may be user settable, so may not reflect the true sender. In this case, it shows the original sender of the message.

Sender: The sender. This is inserted by some systems if the actual sender is different from the text in the From: field. This makes email more difficult to forge, although this too can be set by the sender. There are other uses for a sender field. In the example above, the sender is set to the list owner by the mailing list system. This allows error messages to be returned to the list owner rather than the original sender of the message

To: Who the mail is sent to. This may be a list or an individual. However it may bear no ralation to the erson that the email is delivered to. Mail systems used a different mechanism for determining the recipient of a message.

Cc: Addresses of recipients who will also receive copies.

Subject: Subject of the message as specified by the sender.

Message-id: A unique system generated id. This can sometimes be useful in fault tracing if multiple copies of a message have been received.

Reply-to: Where any reply should be sent to (in preference to any electronic mail address in the From: field if present). This may be inserted by the sender, usually when they want replies to go to a central address rather than the address of the system they are using. It is also inserted automatically by some systems

X-Mailer: Any field beginning with X can be inserted by a mail system for any purpose.

When using a reply facility it is important to check where the reply is going by looking at the header of the outgoing message displayed on your screen. If the message has been forwarded to you, the reply will often go to the original sender and not the person who sent it to you.

Last Updated 18 Aug 2000. Please mail any comments to C.B.Bayliss@bham.ac.uk