Your ISP has possibly allocated you an IP address that someone has previously used to send out vast amounts of spam, with the result being that the address has been 'blacklisted' by the filtering systems that many email services used.
Changing your IP address usually involves nothing more than disconnecting your router from the phone line (or cable), waiting a minute or two and then reconnecting. I can't guarantee that it will fix the problem but it's certainly worth a try. Start by going here to view your current IP address:
https://whatismyipaddress.com/
After disconnecting and reconnecting, return there to check that it's changed.
It's also possible that a spammer has sent out millions of emails that appear to have come from your email address. Spammers like to use genuine addresses in the 'from' and 'reply to' fields of their messages. They harvest addresses for that purpose by hacking into the databases of websites like AB to find them. (NB: I'm NOT suggesting that this site is insecure; I'm simply pointing out that you've probably provided your email address to LOADS of different websites and your email address might have been harvested from one of them).
If that's happened the best thing for you to do is to create an 'alias' address with Yahoo. e.g. if your main address is '
[email protected]', you can set things up so that you can also use '
[email protected]', with mail sent to both of your addresses arriving in the same inbox. You could then select the new address when sending outgoing mail, so that it didn't get caught by spam filters.
https://help.yahoo.com/kb/SLN15953.html?guccounter=1