General Info : Common Messaging Formats

For most organizations, e-mail messaging has become an increasingly important mode of communication. However, not all organizations use the same type of messaging systems. In this blog post, we will see the format of e-mail message and some of the common messaging formats used.

Format of an e-mail message

Internet e-mail messages follow the format standards that are defined in RFC 2822. A message is made up of header fields and a body. The header fields are collectively named the "header" of the message. The body of the message is optional. A message can be sent without a body, but not without a header.

The header contains a sequence of lines of characters that have a special syntax, as defined in the RFC 2822 format standard. The body contains a sequence of characters that follow the header and that are separated from the header by an empty line (that is, a line that has nothing before the Carriage Return and Line Feed [CRLF]).

Header fields are lines that are composed of a field name followed by a colon (:), followed by a field body, and ended by a CRLF. A field name must be composed of printable US-ASCII characters (that is, characters that have values between 33 and 126, inclusive), except the colon. The colon is used as a separation character.

A field body may be composed of any US-ASCII characters, except for the CRLF. However, a field body may contain a CRLF when used in header folding and unfolding. Folding is when, for convenience, a single line appears on multiple lines. Unfolding is the reverse of this. All field bodies must follow the syntax described in sections 3 and 4 of the RFC 2822 format standard.

The body of the message may include one or more sections. Each body section is separated by a boundary. The boundary parameter is a text string that begins with two hyphens (—).

Now lets see some of the common messaging formats used…

Plain text

A plain text message is the most accepted form of messaging format. All e-mail message readers can display text messages in plain text format. However, plain text messages cannot display colors, different fonts, or emphasis such as bold or italic text.


Rich Text Format (RTF)

Exchange 2000 uses RTF messaging for messages that are delivered between Microsoft Outlook users. RTF displays colors, fonts, and formatting. However, RTF is only readable by Outlook. Exchange 2003 RTF format is different from the RTF format that is used in a word processor program such as Microsoft Word.

Note If a recipient receives a file attachment named Winmail.dat in their e-mail, that domain has an RTF incompatibility issue. To work around this issue, you must configure a rule that makes sure that messages that are sent to that domain do not use RTF format.


HTML format

HTML mail is a recent implementation that makes it possible to display rich content in a message. When you use the HTML mail format, the message is sent as an HTML page, complete with tags to change the appearance of the text. The recipient's e-mail client program then formats and displays the HTML. The major issue with HTML text is that not all e-mail client programs support HTML text. If the HTML e-mail message is not displayed correctly, the message can become unreadable.


Plain text and HTML

Exchange 2003 can send messages to external domains as both plain text and HTML. This format appears correctly on both types of client. However, the messages become two times as large and processing takes longer. You may be able to view both the plain text and the HTML in the replies to the message. This behavior frequently occurs in discussion groups where people have posted messages by using both plain text and HTML.

MIME and uuencode

MIME and user-to-user encoding (uuencode) are two different methods of sending binary attachments with messages. Early e-mail client programs used uuencode as the default message format. However, most current e-mail client programs support MIME. You may have to communicate with a domain that continues to use uuencode. In this scenario, you can configure a rule to deliver messages to that domain using the uuencode format.

Message text word wrapping

Although this format is not strictly an e-mail messaging format, some earlier versions of e-mail messaging clients require that a line break is placed after the seventy-sixth or seventy-seventh character. If you do not perform this procedure, those clients can only view the first 76 characters of each line. As a result, large portions of the message may not appear.