What Is a MIME Format in an Email?
Basic Internet email protocol known as Simple Mail Transfer Protocol, or SMTP, only supports the transmission of 7-bit ASCII characters. This limits the size and types of messages that can be sent. Multipurpose Internet Mail Extensions, or MIME for short, surpasses SMTP by allowing email messages to include multiple objects and 8-bit binary data. MIME is only limited by the ability of specific web browsers to decipher its content.
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Definition
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MIME is an email encoding standard enforced by the Internet Engineering Task Force, or IETF. MIME extends SMTP by allowing the transmission of multimedia and other binary data with ASCII-formatted encoding. This is accomplished by using MIME types with markup tags to describe the contents of the document.
How It Works
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Generally, the sender's email program assigns MIME types and subtypes to an email message. The receiver's email program uses a standard set of document tabs to decode the message. How each element is decoded depends on the type of Internet browser installed on the receiver's computer. Web browsers maintain different decoding schemes, although most will include elements that are common to HTML's hypertext transfer protocol. Non-text items use the base-64 encoding scheme.
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MIME Requirements
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MIME-formatted email messages contain a header and body. The header relays information about the MIME version and data types stored. The body of the MIME message is optional and may involve four elements. The first is the content-type, which specifies the type and subtype of data included. Next, the content-transfer-encoding header defines how email software will convert the data in the email. The content-disposition header specifies the content types encoded in the message. Finally, the content-ID provides identifying information for multipart email messages.
MIME Types and Subtypes
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MIME types and subtypes constitute the components that users may include in an email. The Internet Assigned Numbers Authority, or IANA, has defined 10 binary data types, including application, audio, example, image, message, model, multipart, text and video. Subtypes describe the characteristics of each binary file. For example, "Plain" or "HTML" further delineates the MIME type "text."
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References
- Microsoft Press Computer Dictionary, Third Edition; Microsoft Press; 1997
- Hunny Software: The MIME Information Page
- About MIME and Content Conversion in Exchange 2000 Server and in Exchange Server 2003
- Internet Assigned Numbers Authority: MIME Media Types
Resources
- Photo Credit Stockbyte/Stockbyte/Getty Images
