Can't add Comcast email to Mac OS
I'm posting for my dad. The problem began last week when he stopped being able to send email from his Comcast.net account on his MacBook Pro. Changing the SMTP server settings wasn't helping, so I tried a troubleshooting suggestion of deleting the mail account with the intent of immediately adding it back. This turned out to be a huge mistake as I have been unable to add it back to his Mac. I've tried restarting the computer multiple times, changing the password on the Xfinity site, I've tried to add it via the Mail app and I've tried to add it via System Preferences/Internet Accounts. It just thinks and thinks and thinks and then says (after 20+ minutes) "cannot verify username or password." I KNOW the username & password are correct. At one point after many tries I was able to add the account on the Mail app but it would only add as POP, not as IMAP, which was annoying, but he was prepared to live with it. However, that also stopped working and I deleted it thinking at least I could add the POP account back, but now I can't add it as POP or IMAP no matter what I do. I've also tried deleting a bunch of Mail settings in his Library but that hasn't worked either.
Meanwhile, the Comcast email (IMAP) works perfectly on his iPhone.
Is this a Comcast problem or an Apple problem? Admittedly his computer is about 10 years old, but everything was working fine until last week.
Thanks for any suggestions.