someone sent me a .mdb attachment today and i couldn't open it in outlook. no amount of searching the options could change this behaviour. i searched online and found a few microsoft kb articles about it, and how to change the registry to add exemptions to the 'Level 1' list of file extensions, which outlook regards as unsafe. i did all the steps in the article but it still didn't work. then i found this GREAT outlook plug in which adds a tab to the outlook options and allows you to configure how outlook handles all the attachments.
How on earth MS forgot about this is beyond me. they actually suggest that you ask the person who sent it to rename the file with a bogus extension and resend the attachment. surely it is sufficient to force users to save the file to disk and then open it themselves by choice. sheesh!