"For future information, if your email app stops working the first thing to do is to see if you can still use your email account when using a web browser.
If you can then the best advice is to do nothing such as changing passwords or deleting and resetting up accounts as this invariably causes more problems than it solves, as you have now found out."
This is good advice. When out and about - particularly (but not exclusively) when overseas, I randomly get an error message on my BT internet accessed via the Mail app on my mobile phone, asking me to re-input my password because the App cannot connect. Of course, when I do this it makes no difference. This can happen whether connected via phone data or via hotel or business WiFi. It resolves itself when I move to a different hotel or business WiFi or go to a different location, so I can only conclude that the BT servers refuse to respond to some servers for hotel/business WiFi or mobile phone data.
This never happens with my gmail email, so I guess BT must keep some sort of blacklist of servers it will not respond to and which is too broad in its scope.
