We have moved about 20 users to O365 in a Hybrid environment. I have moved one of the users back onto our on premise Exchange 2010 environment. His Outlook is working fine, but his iPhone stopped working. We have removed all profiles, reset his phone, etc., but still nothing. We disabled active sync and re-enabled it and setup his phone to point to the proper url (our OWA url) that all other on-premise users have for iPhone, but it still doesn't work. We had him log into OWA from his browser on his PC and iPhone and both work fine. We tried a different on-premise mailbox on his iPhone and it worked fine, so it appears to be something with his account. I have looked at the attribute editor on his AD account, but there is nothing that jumps out at me as a problem. Anyone know of any gotchas for migrating back from O365?