Quick background and I get into details if more info is needed.
We are moving to O365 and have two E2K10 servers left (1 mailbox and 1 CAS). Because we use AD Connect to sync to Azure AD we are keeping one server (E2K16) on prem for management purposes. Currently all of our user mailboxes are on O365/Exchange Online. at the end of the day the two E2K10 servers will be decommissioned and only the E2K16 server will remain.
I installed the E2K16 server last night and all is working but when users open outlook they get the error attached. Even though outlook is pointing to the O365/EXO servers for some reason its also trying to contact the new server as well.
I added our current SSL cert that was on our E2K10 server to the new E2K16 server and added the services to use that cert but it seems like outlook is trying to point to the local name and not whats on the cert.
I am not sure where to go from here. When I did this for our E2K10 servers many years ago, once i added the cert and the services to that cert I stopped getting errors.