As BPOS tenants are moved into Office 365, mobile devices will lose their ability to receive email content, messages, calendar requests, etc. This is due to the BPOS mailbox MOVING from BPOS into Office 365. Because of this, at some point during the BPOS Transition Weekend your mobile phone will no longer be able to send/receive email, at least for your BPOS Messaging profile. As an administrator and/or end-user you should make sure to identify the following screenshot, which tells you that your BPOS mailbox has moved into Office 365 and you will need to reconfigure your phone, either manually or via ActiveSync to use the new Exchange Online 365 messaging configuration settings.
When you see this error or something similar on your mobile device, you know that your mailbox has been moved into office 365
To learn more about how to reconfigure your mobile device, please use one of the following links, which are for Small Business and Enterprise customers: