The default username is admin and the password 1111.
You and the people on your network are the only people who can access the printer, so your frustration is misplaced if you are trying to blame Xerox or your printer itself.
If it worked and stopped, something changed, and if neither you or anyone on your network changed something on the printer, then something on the LAN (Gateway/DNS) got changed, or on the mail server (Password/Port/Encryption)
And if you enabled HTTPs on the printer, then the time will need to be within 3 minutes of local if you are using any common mail server (Office365/GMAIL/Yahoo). And the time on the printer can run slow or fast just like any clock if it is not set to use NTP and a reliable time server.
Ans since it appears you must have locked yourself out of the printer after repeated failed logins, you will need to reboot the printer to gain access again