When e-mail was first created, MIME did not exist. MIME (as the name implies) is an extension of the e-mail standard. Nowadays, almost every e-mail message that is sent over the Internet uses MIME in some form or another -- even if they don't have any embedded file attachments or HTML formatting.

The concept behind the MIME format is simple: instead of assuming that e-mails are plain text, MIME allows the sending computer to specify the specific details of the content itself (such as its content-type and encoding type). MIME also allows for a "multi-part format," which I'll discuss in more detail later.

To give you an idea of the differences between MIME and non-MIME e-mail, let's look at some examples of the two. The first is the complete text of a standard e-mail, as defined by RFC-822, and is the simplest format for an e-mail message. The second is an example of the same e-mail using the MIME format: