When you're setting up your Kindle Fire for BT Business email make sure you're using these mail settings:
Incoming server settings
Server name: outlook.office365.com
Port: 995
Encryption method: SSL
Outgoing server settings
Server name: smtp.office365.com
Security type: STARTTLS
Port: 587
Requires sign in: needs to be ticked
Then input your email address and password.
