When I log on to my BT account, it has always remembered my BT ID/email address, I just have to enter password. How can I set my BT Yahoo email account to do similar? I always have to log in with email address and then password.
It is probably your web browser that is retaining the email username on your BTID. If you do an Internet search for "remember username passwords" for the browser that you are using it will tell you how to re-activate that facility.
If the the browser won't retain the user name and password the best way to do it is to use an email client. This will automatically log on, retrieve your email and download them onto your computer then log off every time you use the email client.