The ability to create e-mail messages with audio and other non-textual contents has been around for a while, but almost always as part of a vendor-specific ``solution.'' This means that you can't create a message under a NeXTstep system with PostScript information and Lip Service (NeXT's audio e-mail) and directly handle the same message on an HP 9000/710, a Sun SPARCstation IPC, and a Silicon Graphics Iris. That's a problem that MIME helps to solve.
MIME, the Multi-purpose Internet Mail Extensions, is a freely available specification that offers a way to interchange multi-media e-mail among many different computer systems. MIME supports not only several pre-defined types of non-textual message contents, such as μ-law audio, GIF files and PostScript images, but also permits you to define your own types of message parts.
The MIME specification is given in the Internet ``Request for
Comments'' document RFC 1341. It's one of the more readable RFC
documents, so if you're interested in the details of MIME, I suggest
that you find a copy and read it. (See section for
information about how to obtain copies.)
MIME isn't specific to MH; there are other mail systems that support MIME. MH offers one widely available implementation of the MIME specification.
If you're curious about what the MIME representation of a message looks like, try typing list -noshowproc after you've run edit mhn on a draft and before you've sent it:
What now? list -noshowproc
It's also possible to view raw MIME by using a command like this one:
% show -noshowproc