Multipurpose Internet Mail Extension (MIME)

Multipurpose Internet Mail Extension or MIME is an Internet standard that extends the limited capabilities of email messages. As such, it allows email messages to support text other than ASCII, as well as attachments like audio, video, images, and applications.

This allows message bodies to consist of multiple parts and heaters to be specified in non-ASCII character sets. Mail messages with MIME formatting are typically transmitted or sent with standard protocols like Simple Mail Transfer Protocol (SMTP), Post Office Protocol (POP), and Internet Message Access Protocol (IMAP). Despite this, its content types are also important in other communication protocols.

What is MIME used for?
Considering what MIME is, it’s easy to see what it’s used for. Traditional email messages sent over the Internet using SMTP consist of a header and body, both encoded using 7-bit ASCII. This presents several limitations when it comes to sending emails.

MIME was designed to extend these limited email capabilities beyond only supports ASCII characters. As such, all manually composed and automated emails are transmitted through SMTP using MIME.

The MIME standard also defines what content types are important in communication protocols like HTTP for the World Wide Web. In this case, the data is transmitted in the form of email messages through HTTP even though it’s not an email.

Typically, the features provided by MIME to email services include:

  • Support for multiple attachments in a single message.
  • Support for non-ASCII characters.
  • Support for layouts, fonts, and covers which are categorized as rich text.
  • Support for attachments which can include anything from executables to audio, images, and video files.
  • Support for unlimited message lengths.

The MIME standard defines five additional extensions to SMTP message headers, supports multipart messages with more than two parts, and allows the encoding of 8-bit binary data such as image files.

These MIME extensions are implemented as fields within the email message headers. These fields define the following:

  • Content-type.
  • Content transfer encoding method.
  • MIME version number.
  • Content ID.
  • Content description.

How does MIME relate to Email?
If one has regard to what MIME is used for, it’s easy to see that it’s vital for proper functioning emails. Without it, email with attachments, different layouts, and no limits on message length would not have been possible.

In simple terms, email as the world knows it today, would not be possible without the MIME standard.