when trying to get email, getting server rejected login. Verify username/password are correct

I'm having the same issue with my att.net email. I've tried logging in too many times and now I guess it has put a block on my account?

Depending on your email client, you may need to get a "secure mail key" from the profile section of your login. Then use this as your password in the email set up of your client. I just got it to work on Thunderbird.

https://www.att.com/support/article/email-support/KM1240308/

s2in954's info worked for me on my iMac! I created a new key, used it for the password and the account was created.