Office 365 imposes a (pretty generous) limit on the amounts of connections it allows for a given email address.
If you want to make sure you can smoothly use your Office 365 account with BlueMail, it is recommended you remove it from other clients that you do not use for this account any longer.
To do so, sign in to myaccount.microsoft.com, go to Devices, and disable the connections that are no longer needed.
