Registry change to allow MDB files in Outlook

1.  Close Outlook. 
2.  Open the Registry Editor. 
3.  If you are using Windows XP/Office 2007, expand the branches to HKEY_CURRENT_USER\ Software\ Microsoft\ Office\ 12.0\ Outlook\ Security
4.  Create a new string value by selecting New and then String Value from the Edit menu.
5.  Name the new value Level1Remove. 
6.  Double-click the new Level1Remove to edit it, and enter the filename extensions you'd like to stop Outlook from blocking. Extensions should be typed in lower case, without the dots (.), and separated by semicolons (;). For example, type 
exe;mdb;vbs to allow .exe, .mdb, and .vbs attachments, respectfully. 
7.  Click Ok and then close the Registry Editor when you're done. 
8.  The next time you restart Outlook, you'll now be able to open previously-blocked attachments.