David - I've had this problem a lot. I've found that the easiest solution is
to save a temporary copy of the database somewhere (like your desktop), then
change the file extension to something else (like .test). You'll probably get
an error message, but that's OK. Attach this document to your email, and tell
the recipient to save the file, then change the extension back to .mdb before
attempting to open. Once you've sent the email, you can delete the copy on
your desktop.
This drives me CRAZY about Outlook...I hate that it makes the decision about
whether a database is safe to open. If I know where it's coming from, and
that it's safe, I should be able to override this blocking feature.