I have noticed that some list members sent mail with the main part of the
message as an attachment.
Most of the time this is just fine but I can't see the message when I pick
it up with my palm pilot.
Likewise, sending with HTML format (the default for most Micro$oft programs)
can be a real pain for some readers.
(On the plus side - it allows colors, fancy fonts, blah- blah-blah for mail
readers that can see this format)

This link discusses these issues and describe how to set come common mail
programs to send plain text.
http://www.geocities.com/CapitolHill/1236/nomime.html#examples
I'm sure there are much better links but this was the first relevant hit on
www.alltheweb.com.

Mark Browne