[H-GEN] Attachment sent as .pdf arrives as .dat - any clues?

[moondrake at aanet.com.au]

Hi All,

I'm hoping the combined sysadmin experience on the list might be able to
help confirm my suspicions about this issue.

Here's the problem.  I send a plain text e-mail with a PDF attachment,
using thunderbird (1.5) on my opensuse 10.2 box to a bunch of recipients
(all in the 'to' field).  My smtp server (sendmail) sits on a debian box
one door down.

Two of the recipients (that I know of) complain they can't open my
attachment because it's a '.dat' file and they don't know what to do with
that.  However, when I ask them (on a hunch) to open the attachment using
acroread, it works.

So my question is - what has changed the file suffix from .pdf to .dat?

I know for a fact that one of the recipient's mail servers is M$ Exchange.
 I suspect the other one is too (because I know their IT consultant is
windows-only).  I suspect (for no good reason really) that M$ Exchange is
the problem.

I know all about the winmail.dat files you can get from outlook users who
send e-mails in rich text format.  But I was using t'bird and the e-mail
was plain text.  I could only find one instance on the net of a similar
problem - but it had no clear solution or diagnosis
(http://bink.nu/forums/2/16703/ShowPost.aspx?PageIndex=2&PostID=16703).

Any clues as to what the problem might be would be appreciated.

Ta,

David