The only way I can access my email is using web mail. If I try and access mail using the app in an Amazon fire tablet the response is "invalid email address or password” The response is the same when using the Gmail or Outlook app on my Samsung mobile phone. Contacted BT and their response was “We know it is a problem, but it is not our problem, it a problem with the Yahoo mail servers.” They had no idea when the problem might be fixed. Another good reason not to use BT yahoo mail. 😠
Don't change anything, give it a day or two and it will start working again.