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, please visit your account on Office 365's web client. From there, please go to Settings (Options) | General | Mobile Devices | Delete the connections that are now unneeded.