How Does MIME Work?

Multiple Internet Mail Extensions

MIME, an acronym standing for "Multiple Internet Mail Extensions", is an Internet messaging standard that allows email to contain multiple parts. Before MIME came into usage, all email had to conform to the RFC 822 standard, which only allows messages to contain plain text. MIME was created as a means to reinforce this standard, still transferring messages that are written in plain text but also allowing for attachments in different formats. The way that MIME handles a message depends on whether the message is comprised solely of text or if there are images or other components included with it as well.

Dealing with Plain Text Messages

If an email message consists of nothing but plain text, MIME will transfer it in exactly the same way that RFC 822 would. The message will be sent as a single ASCII file to the recipient's email account, where it will then be displayed as a text email. No additional sorting or configuration will occur.

Dealing with Messages Containing Multiple Components

Should the email message include HTML components, images, or have any files attached to it, MIME handles it differently. The message is broken down into components and sent, with the core text of the message still being sent as ASCII text via the older RFC 822 standard. When the message is received in the recipient's email account, the MIME formatting tells the email client that the data needs to be configured in a specific manner. This allows the email client to properly display the HTML and images that are included in the email, and properly display any attachments so that they can be downloaded onto the recipient's computer. All of this configuration information is stored in the MIME header that is attached to the email message, which is read by the email program before the rest of the email is displayed.