How to clear a badly cached Outlook email address
Outlook caches Microsoft Exchange email addresses based on more detailed information than just the email address itself. Sometimes when an update is made to an Exchange account, that detailed information no longer matches the cache and Non-Delivery Reports are received.
The NDR will contain text similar to this:
Remote Server returned '550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found'
To prevent this problem, the cached address must be removed from Outlook.
Start typing the name of the badly cached address, then click the X next to it. To insert the correct address, click To or Cc and find the name in the Address Book.
If this does not solve the problem there are two possibilities:-
1) You may need to update your local copy of the Address Book. Click File, click Account Settings, click Download Address Book and then click OK:
2) The Address Book on the server has not been updated yet, you can wait 24hrs or contact the helpdesk.