If you are on the BTMail system check you have the correct settings as per this link
and if on the BTYahoo email system you could try these settings.
Thanks. This link is telling me the incoming server is imap.mail.yahoo.com . The one that autmatically populates is mail.btinternet.com
How do you edit the incoming server in the mac mail app? It lets me edit the outgoing but the incoming is 'greyed' out.
I don't have a Mac so can not be specific but you may need to delete the account again and re set it up. When setting it up use the maunual option so that you can enter the correct server settings.
Thanks for your help. I fixed this by adding an 'other' account rather than a 'Yahoo' account (which I have always done, historically). A box came up with an error message but it allowed me to type in the server settings that your link directed me to. Can't thank you enough....have been struggling with this since Feb 22nd!!!!