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