<p>The BT Sport app closed on 12th October and has been replaced by discovery+. <a href="https://community.bt.com/t5/TNT-Sports-on-TV-Online-player/The-BT-Sport-app-is-closing-on-12th-October/td-p/2312034">Find out more about activating TNT Sports on the discovery+ app</a>.
If it wasn't for the fact that BT would charge me to keep my existing email address I'd move to a client that works properly
BT do not charge you to keep your email address should you want to leave BT. Your email account would be "downgraded" to BTMail basic, which mean that you can only access it using a web browser and not using an email client/app.
If you want that functionality you would need to take out a BT Premium email account costing £7.50 per month.