Dave has an email account that has been hacked and now he's getting requests for new passwords. He found out by noticing the forward codes after the request. Leo says that it's a common scam. Fortunately, Spectrum changed his password for him. But now Apple Mail can't make a connection with the new password. Leo thinks that the email client may not like the password. So Dave could try changing the password again. But Spectrum may have turned on a feature that limits what Dave can do to protect him. What Leo suggests is to delete your email account and then set it up again.
Also check your Apple Mail logs. They are very detailed on what's going on with your account. Open connection doctor and enable "log activity." Then go through the process of logging in again. Then check the log and see what's going on. You may have to google the error message, but it's a useful tool for troubleshooting your internet and email issues.