Mark is having issues with his Verizon email because it's part of Yahoo and now Verizon doesn't support it. He can't log in, and Verizon doesn't seem to care to fix it. Mark could try logging into Yahoo mail directly. Leo says Mark should make the move to another email provider like GMail.
The chatroom recommends this technote by Yahoo - https://help.yahoo.com/kb/verizon/mail-for-desktop/learn-fix-issues-connecting-verizon-yahoo-mail-pop-mail-client-sln3792.html
The key is to make sure to have all of the settings right. Here's a page that talks about that - https://help.yahoo.com/kb/verizon/mail-for-desktop/pop-settings-sln4724.html