Hi. Just posting here with a solution if anyone has been having the same frustrating experience as me migrating from Yahoo email to the BT email app on Android. Try as I might, although the browser transfer (webmail?) was seamless and worked perfectly, opening the app I could not sign in and was persistently told my username and password were unrecognised. Completely inexplicable. Turns out that BT's password criteria no longer accepts certain special characters (e.g. '£') and it was this that was causing the problem. So a password reset fixed it, and no inanimate objects in my immediate vicinity were harmed. Anyway, hope this helps anyone out there in a similar predicament. Cheers.