I have succesfully migrated an exchange 2010 environment to an exchange 2013 server.

Now I am finding in my logs this message:

SMTP rejected a (P1) mail from 'HealthMailboxb91a20da4d8649a68abbb80cb44c9d83@<my domain>.local' with 'Client Proxy <my server>' connector and the user authenticated as 'HealthMailboxb91a20da4d8649a68abbb80cb44c9d83'. The Active Directory lookup for the sender address returned validation errors. Microsoft.Exchange.Data.ProviderError

What I checked:

- This healthmailbox has in the AD the permission to 'send as' for SELF
- I have noticed that the UPN is set as "...@<my domain>.be" (which we use for standard emailadresses), I have changed this to "...@<my domain>.local" but after a few minutes it automatically restores itself (?) to the previous value..

Any help on this matter? I have read I can delete the entry from the AD and restart  the exch monitor service but I'm not sure if this won't break anything as this is the only server running all services.

If someone would have the same problem, I used the following solution which apparently fixed it..

http://serverfault.com/questions/527404/users-unable-to-send-over-smtp-after-upgrade-to-exchange-2013?answertab=active#tab-top

• Marked as answer by Amit TankMVP, Moderator 5 hours 58 minutes ago