If you've entered the wrong address into the Windows Vista Mail client, you might have problems getting rid of the wrong autocomplete entries in the list. There's a couple of things you can try to delete the entries in the list. First, you can use the Down Arrow key to select the incorrect entry in the list, and then use the Delete key to remove the entry. This usually works, but for some people it just doesn't work, the wrong addresses come back. What you can do is completely wipe the auto-complete cache in the registry. Start by completely shutting down Windows Vista Mail. Open up your registry editor by typing in regedit into the start menu search box, and then browse down to the following key:

HKEY_CURRENT_USER\Software\Microsoft\Windows Mail\Recently Used Addresses

Once you are there, look for the entries in the right-hand side. Delete everything other than the (Default) key.

Now you can restart windows vista mail, and all of your auto-complete entries should be gone, including the wrong ones. Derived from mtnpilot's thread on the forum.