2.2.3.4.2 Apple File Formats

[RFC1740] and [RFC1741] specify the use of the MIME Content-Types "multipart/appledouble", "application/applefile", and "application/mac-binhex40" to encode files that originate from a Macintosh operating system, to preserve additional data that might be available for these files in that operating system. MIME readers SHOULD preserve this additional data for attached files to enable full support of Macintosh-based client applications.

In particular, the Attachment object content that is stored in the PidTagAttachDataBinary property ([MS-OXCMSG] section 2.2.2.7) MUST contain a MacBinary stream (1). This stream (1) format incorporates both the resource and data forks, as well as certain metadata.

Note that MIME analysis of "application/applefile" attachments is specified differently, depending on whether the "application/applefile" MIME entity is a subpart of "multipart/appledouble.