[imp] attachment MIME types

[Liam Hoekenga]

We're having an issue w/ the MIME types assigned to attachments with 
messages composed in IMP. 

Several help-desks at UMICH use "Footprints", and messages w/ 
attachments of type "message/rfc822" are a special case in Footprints.  
We had a user attach a text file (with a .txt extension) to a message 
using IMP, and it was identified as "message/rfc822", and the resulting 
entry in Footprints confused the admins of that service.  I can't 
replicate the problem.  I've tried to replicate the environment (same 
browser, attaching a file from the same source) and every time I try, I 
get a file of type "text/plain".

Anyhoo.  What I'd like to know is how an attachment's MIME type is 
determined when composing mail in IMP.  I think I asked a similar 
question about a year ago (where excel files were getting identified as 
word files despite their .xls extension) and was told that the user's 
browser determined the MIME type of the attached file.  Is that indeed 
the case? 

Liam