I'm getting a bit fed up with this problem. I used to use Windows Live Mail until about a year ogo when for some reason it could not connect to the BTYahoo server. I tiried using Outlook, but that is mainly for bussiness, I tried the Win 10 Mail, but that is waste of time. In the finish I settled on Thunderbird, that gives a very similar experience to Windows Live Mail.
However in December, I started having problems with my account. Firstly it was compromised, some of my contacts were getting emails with my address on from Dropbox. I received an email from a contact telling me about the Dropbox email, and my email worked fine. Then a hour later Thunderbird could not access the server. BT recommended that I change my password, although they said they couldn't find any problems. Now today, Thunderbird cannot access the BT server again, I have checked the password and it is correct, but still cannot access the server.
Another strange thing I have a sub-account, that has never been affected it worked fine with Windows Live Mail and now still woirks with Thunderbird.
There have been problems with the BT IMAP/POP servers stopping email clients from accessing the users email account for years. The advice from forum users is to do nothing such as changing passwords or deleting and resetting up accounts as this invariably causes more problems than it solves.
If you are still able to access your email via webmail it is obviously not a problem with your email accounts or with your password, hence the advice not to do anything. The problem usually resolves its self in a day or two.
As regards your email being compromised. Yahoo/BTYahoo had a massive hack about five years ago when millions of email accounts were hacked. At that time your contacts details would have been harvested by the hackers and they are now able to use them any time that they wish.
When the hackers send emails to your contacts they are not using your email account. They are "spoofing" your email address to make it appear that the email is coming form your account in an attempt to make the email appear genuine to your contacts and as such there is no point in changing your password in an attempt to stop it from happening.
It is however good practice to change your password after an email account has been hacked in order to stop the hackers getting back into your account.
I had never been told that before.
I raised a complaint and BT did check everything was in order.#
It did seem odd though, about an hour after I raised the complaint I receved about 30 emails en block.
Another odd thing is I have a sub-account that the wife uses and that has never been compromised and has always seen the BT server.