Exchange try to deliver local instead offer smart-host for deleted/changed email address

Copper Contributor

Don't really know if this is the right place to ask,
but I have a problem with our newly set up Exchange Server (2016)

We have internal and external personal, so I set the Exchange up as an intern-relay and a smart-host for sending. It works fine.

Internal users have the email address registered in exchange
External users have the email address registered in Exchange. (The messages here are only forwarded to a different mailbox to archive them. Their normal email address ( is not registered in exchange.)

It worked all fine. But now I wanted to switch user1 from internal to external.

So I disabled the mailbox and made a new one fort the same user with the external address (
If internal users email that user with the address it should go over the smart-host, because there is no user anymore with this address.

But I get this error message:
Remote Server returned '550 5.1.11 RESOLVER.ADR.ExRecipNotFound; Recipient not found by Exchange Legacy encapsulated email address lookup'

I tried to delete the lagacyExchangeDN fort that user in the AD, but it keeps refilling it and I don't really know what else to try.

I basically want the gone from exchange, so he sends emails for that user over the smart-host and don't try to deliver it local but somehow the address is still linked tot hat user.

1 Reply



I am unsure what you are doing with the old email address,, after converting them to


I would have maintained the old address user1@ by adding it as a secondary address to ex.user1@  I would have documented the legacyExchangeDN on the user1@ mailbox and added it as a x500 address to the ex.user1@ mailbox.  But you deleted the user1@ mailbox so you can't get the legacyExchangeDN now.


However, with all that said what it sounds like you are having an issue with is the autocomplete entry.  Try clearing that in Outlook when creating a new message.  Start typing the recipients name, you should see the users name show up, click the X to delete the entry.  Next, choose the user from the GAL or try typing the new email address in full.  You'll have to do that for everyone individually.  If you carried over the legacyExchangeDN from the old mailbox you would not have to do this.