message/partial

Email's answer to IP fragmentation, from MIME's founding document RFC 2046: a large message split into numbered pieces, each carrying id, number, and total parameters so the receiving client can reassemble the original. It solved a real 1990s problem — mail gateways with hard size ceilings — and then became a security problem itself, since an attachment split across fragments is invisible to any scanner that inspects messages one at a time; mail filters commonly quarantine the type outright for exactly that reason. With modern message-size limits measured in tens of megabytes, it is a fossil: formally valid, still in the registry, and best treated as suspicious when it appears.

Defined by RFC 2046 · IANA registration. Registry facts from the IANA media-types registry via mime-db.