Any version of LetMobile, specifically when a company with users is transitioning from a company mail server to Office 365
What needs to be done if a user is switching their mail account over to Office 365?
If a user is switching over to use Office 365 instead of your Exchange Server then there needs to be a Mail Server Exception added (for that particular user) in the LetMobile Admin Console.
This is done under General Settings --> Mail Server Exceptions. The new exchange server address for these users would be outlook.office365.com.