Email Message Format

A variety of data like; sound files, images and other binary information, etc., are included into email messages--which can be formatted by adding specific descriptions to all parts of the message.

For example; messages composed in "rich text" or HTML format may include WAV sound, GIF images attachment, etc.--the message will consist of 3 parts, so that a mail reader (MS Outlook or Eudora, etc.) can display the message in "rich text" or HTML with the image and play the sound WAV file--which are not included in normal email messages.

Hence, a standard format known as MIME (Multipurpose Internet Mail Extensions) has been created to describe the message parts and mail program conforming to this standard will be able to describe its own messages and interpret messages created by other systems.
 

(MIME) Multipurpose Internet Mail Extensions

MIME encoded messages consist of many parts--each part is allowed to be described in detail and some parts encoded. The purpose of MIME is to describe the many parts of an email message, such as attached sound files and images.

MIME messages may include a plain text message and a GIF image--because GIF image is binary data consisting of 8 bit characters. To get the GIF image data to pass through the Internet--Base 64 is used to encode the data into 6-bit characters.

Read more about...
Email Message Structure
Mail Servers Protocol
Simple Mail Transfer Protocol
Post Office Protocol
Internet Message Access Protocol
Binary data encoded message