In the hybrid environment when you have users in both - on premises and in the Office365, you could end up with users that cannot configure new mailboxes after migration to the cloud.
This is because user accounts could have AD homeMDB and homeMTA attributes set.
Go to ADSIEDIT.
Go to the Default Naming Context
Search for the user object.
Go to the properties and search for homeMDB and homeMTA attributes.
If they are not empty, delete data that are in.
Then try to configure Outlook again.
This is because user accounts could have AD homeMDB and homeMTA attributes set.
Go to ADSIEDIT.
Go to the Default Naming Context
Search for the user object.
Go to the properties and search for homeMDB and homeMTA attributes.
If they are not empty, delete data that are in.
Then try to configure Outlook again.