[tlug] JPEG going out as application/octet-stream

[Jonathan Q <jq@example.com>]

For the first time in a while (since before upgrading 
to RH 7.3 - coincidence?  I think not :-p ) I had 
ocassion to mail a JPEG file (to myself, for testing
a webmail system) and rather than the expected image/jpeg
MIME type, it came out as application/octet-stream.

At first, I was ready to blame the webmail app, since there
had been some other issues involving MIME mail display problems,
but the existing webmail app still saw it as application/octet-stream
(it has no problems with MIME types, so this has reference value).

But when I used the new webmail app to send the exact same file
to myself, it came out as image/jpeg.  The webmail app looks 
innocent, my localhosts look guilty.

I can duplicate it on two different machines, both running RH 7.3.
On one of them, I have two different versions of mutt, and it
doesn't matter which one I use, I get the same thing.

Where do I need to look to hunt this down?  Nothing in sendmail.cf
or .muttrc appears to address this, and if I understand mailcap
correctly, it contains instructions for how to view things that
are received, not how to set the MIME type on outgoing mail.

TIA,

Jonathan