Modern versions of LISTSERV contain a configurable MIME attachment filter that will let you bounce or strip MIME attachments. The filter is configured on a list-by-list basis by using the "Attachments=" list header keyword. (There is no site-wide override.) See the LISTSERV documentation for information on how to configure "Attachments=".

You can also strip HTML attachments from multipart/alternative messages (assuming that there is a plain text alternative in the message) by setting "Misc-Options= DISCARD_HTML" in the list header.  (Note that older lists may have "Language= NoHTML", which is deprecated and should be replaced with the "Misc-Options" setting whenever possible.)  The "Attachments=" keyword setting cannot be used for this purpose, nor can it be used to strip or reject messages of MIME type text/plain (which are always accepted since they are plain text).

A list of registered MIME media types for attachments is kept by IANA and can be found at

https://www.iana.org/assignments/media-types/media-types.xhtml