email always received as att000##.txt

[Guest]

A friend of mine is using outlook (so am I)

Any time he replies to a message, instead of the message
coming in as an email, it comes back to me as the
original email I sent him with an attachment containing
the text of his reply.

the attachment file name always looks like this:

att000021.txt or some other number, but alway of that
format.

Anyone have any ideas how to fix this? can't find in the
knowledgebase

thanks

Dave
(e-mail address removed)