Yesterday we migrated our mail from our Exchange 2007 server to Office 365 Enterprise E3. When we try to set up mailboxes with the new Outlook 2016, we never get the opportunity to enter the new Office 365 login, we immediately get the attached errors. It also gives a certificate error that references our old server (which I did not manage to get a picture of) . Somehow it is trying to access the old mail server and we can't get any further. We flushed dns and that didn't work either. It seems somehow our internal dns is pointing to the old server. How do we get rid of it?