Lexmark CX431
From the home screen, touch > Settings > E‑mail > E‑mail Setup > Disable “SMTP Server not set up” error > On.
To prevent the error from happening again, do one or more of the following:
Here are basic troubleshooting steps if you cannot set up etherFAX in your printer.
Configure the printer for you to send and receive fax messages using the fax server.