Why do I keep having to re-sign in to my BT e-mail account? Multiple times per day on the same device. I have changed my password and re-installed the app.
It could be because the BTMail app is not very good. Try a decent free email app such as BlueMail. It is far better than the BT app.
You most likely won't need them but if you require the server settings when setting it up they are in the following link.