Outlook unable to connect to mailbox after move from Exchange 2010 to Exchange 2016

Question

So I have a strange problem.

We are in the process of moving mailboxes from Exchange 2010 to Exchange 2016 in a coexistence setup.
So far we have moved two mailboxes with success. (account1 and account2) After the move, Outlook needs to restart and it connects to the Exchange 2016 server. Outlook, OWA, iPhone email etc. all working like expected.

Today we moved another mailbox (account3) using the migration wizard in the 2016 ECP just as we did before. The mailbox is moved, we receive an e-mail with overview of the successful and completed mailbox move. After this point in time, the mailbox is hosted on the 2016 server. OWA and email on iPhone work fine, sending and receiving email also works. However, if we want to connect Outlook to this mailbox we just can't get it to work. So we started a test and setup Outlook for this account from a remote pc (outside of the LAN). If we use account1 or account2 we get the expected green checkmarks so autodiscover, certificate is all good and these mailboxes are fully functional in Outlook.
When we want to do the same with account3 that is hosted on the same server, we just can't get it to connect. It will show us this:

an encrypted connection to your mail server is not available

Before the mailbox was moved it worked fine, now we can't get it to work in any version of Outlook. Are there any checks I can perform?

Doing the same steps with account1 or account2 we get the following (in Dutch), all works great so autodiscover is working fine.

Answer 1

I'd try this real quick to eliminate it as a cause:

On the 2016 Server;

Restart-WebAppPool MSExchangeAutodiscoverAppPool 

https://support.microsoft.com/en-us/topic/outlook-logon-fails-after-mailbox-moves-from-exchange-2010-to-exchange-2013-or-exchange-2016-bd3f59ed-c521-4349-5c00-c49717b5e04d