Multipurpose Internet Mail Extensions (MIME) is an Internet standard that extends the format of e-mail to support:

  • Text in character sets other than ASCII
  • Non-text attachments
  • Message bodies with multiple parts
  • Header information in non-ASCII character sets

SMTP supports only 7-bit ASCII  characters. This effectively limits Internet e-mail to messages which include only the characters sufficient for writing a small number of languages. Other languages based on the Latin alphabet typically include diacritics  not supported in 7-bit ASCII, meaning text in these languages cannot be correctly represented in basic e-mail.

MIME defines mechanisms for sending other kinds of information in e-mail. These include text in languages other than English using character encodings other than ASCII, and 8-bit binary content such as files containing images. Mapping messages into and out of MIME format is typically done automatically by an e-mail client or by mail servers when sending or receiving Internet (SMTP/MIME) e-mail. MIME is extensible. Its definition includes a method to register new content types and other MIME attribute values.

MIME headers

The presence of this header indicates the message is MIME-formatted. The value is typically “1.0” so this header appears as

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