If I set up my btinternet.com email in outlook, outlook automatically populates with mail.imap.yahoo.com and mail.smtp.yahoo.com. I discovered this when after a month that stopped working. Impossible however to reconnect uing the recommended mail.btinternet.com for both servers, 993 and 465 ports and SSL and SMTP enabled, all as recommended by BT on web. Their Help Desk on one occasion said to use 993 for both ports and wait 24 hours. Of course, that didn't help. Mircosoft said there is a problem between BT and Yahoo. I'll say. BTW problem only on laptop: tablet and smartphone apps both work fine as does Mail in Windows10. So what's going on and who is to blame?