5.2. MIME Type configuration with mime.types

When you add an attachment to your mail message, Mutt searches your personal mime.types file at ${HOME}/.mime.types, and then the system mime.types file at /usr/local/share/mutt/mime.types or /etc/mime.types

The mime.types file consist of lines containing a MIME type and a space separated list of extensions. For example:

application/postscript          ps eps
application/pgp                 pgp
audio/x-aiff                    aif aifc aiff

If Mutt can not determine the mime type by the extension of the file you attach, it will look at the file. If the file is free of binary information, Mutt will assume that the file is plain text, and mark it as text/plain. If the file contains binary information, then Mutt will mark it as application/octet-stream. You can change the MIME type that Mutt assigns to an attachment by using the edit-type command from the compose menu (default: ˆT). The MIME type is actually a major mime type followed by the sub-type, separated by a '/'. 6 major types: application, text, image, video, audio, and model have been approved after various internet discussions. Mutt recognises all of these if the appropriate entry is found in the mime.types file. It also recognises other major mime types, such as the chemical type that is widely used in the molecular modelling community to pass molecular data in various forms to various molecular viewers. Non-recognised mime types should only be used if the recipient of the message is likely to be expecting such attachments.