Basics of Use: Email Message Format

The email message has a set format. This means every email message has to obey certain syntax and structure rules, and may also use others:

Header and data (body)
     The message is broken into two parts. The header contains all the technical and general information; the body contains the message itself.

Optional and mandatory fields
     The header must include some specific "fields" - for example, it must contain a destination for the message (who is it sent to?). There are some other fields required, and others that are optional.

Privately implemented fields
     Some fields in the header may even be application-dependent: one mail application will be able to understand them and perform the needed action while another will just disregard those fields.

Example:

The opening fields are like paper memos: From; To; Reply to; Cc; Subject There are also key "machine" fields: X-mailer, X-charset, X-sender, X-face. Your mail program usually adds additional fields. Sometimes they make sense to you, and you can even set their value (for example, X-Priority), while others are not set by you. X-Mailer is the name of the email application you are using. X-charset is the character set the message is coded with (like ASCII).

Sending Email

What happens when you finish writing your message and press the SEND button? The message is handled by a Mail Transfer Program. This program contacts the destination server (according to the address) and sends it the message. The server then places the message in the correct mailbox.

The connection follows the Client/Server model, where the mail transfer program is the client, and the destination mail server is the server. The details of this connection are set by the SMTP (Simple Mail Transfer Protocol), which allows the sender to identify itself, specify a recipient, and transfer the message.

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