multipartmixed

Multipart mixed is the MIME multipart subtype used to encapsulate several independent parts within a single message or entity. In formal terms, the correct name is multipart/mixed, defined in RFC 2046, and it serves as a general container for content that does not share a single representation. Some contexts may informally refer to it as multipartmixed.

Each part carries its own headers and body, such as Content-Type, Content-Transfer-Encoding, and Content-Disposition. The overall Content-Type header looks like Content-Type: multipart/mixed; boundary="XYZ". The body consists of boundary-delimited parts, each introduced by a line containing --XYZ, followed by the part’s headers and content. The final boundary is --XYZ--.

Typical usage is in email messages to attach files alongside the main text. A text part might be text/plain or text/html, while other parts can be attachments such as application/pdf or image/jpeg, often with Content-Disposition: attachment and a filename parameter. Binary parts are commonly encoded with base64.

Multipart/mixed is a general container and can contain other multiparts by nesting, for example a part that is itself multipart/alternative to offer several representations of the same content. It differs from multipart/alternative (which groups alternate representations) and multipart/related (which binds related resources to a primary body).

Compliance and handling: most mail clients and servers support multipart/mixed, but correct parsing requires respecting boundaries and decoding of encoded parts. Security considerations include scanning attachments and honoring Content-Disposition to distinguish inline content from attachments.