Lukas Beeler's IT Blog

After migrating several users into our Exchange server, which were first defined as an external contacts (for proper forwarding), everything worked fine.

However, one user was unable to send mail to the new users. It generated a bounce/NDA, and failed to deliver. I first checked the Exchange Server, and everything seemed to be perfect. I then walked this user through the procedure of selecting the user from the address book, and then sending the mail. This worked.

At first, i was baffled, but then i remembered about the external contacts – the external contacts where defined as X.400 addresses, which coexisted with the new users for a short while. so the external contacts had different X.400 addresses than the new users. (I did handle the SMTP Addresses correctly, but not the X.400 ones).

But the external contacts where deleted, and no longer in the GAL or the OAB. But Outlooks address cache for type-ahead finding of contacts is independent of these two address sources. And that’s what the user used. You can delete entries in this cache by selecting them with the cursor keys, and then pressing the delete key. Seems logical, but i haven’t seen this mentioned anywhere explicitly.