I have a big company which consists of 3 different entities. One entity was sold. Currently they still use our ActiveDirectory / Domain Services. They moved to office 365 and are not using our Exchange server anymore. They had a problem that the autodiscovery was pointing the mail settings to our exchange server. I removed there domain from accepted domains and also disabled there mailboxes. They were working fine. After a month they experienced the same problem. What could be the problem?
I was suspecting that since they use our Domain controller we have a CNAME of autodiscover which points to our Exchange Server this is causing the problem.
How can this be solved? Is there a way which it can be solved from the Server side?