Canon MB5400 Series Online Manual page 1089

3420
Cause
Communication with mail server failed.
What to Do
Tap OK on the touch screen of the printer.
Make sure that the settings item for the incoming mail server (POP3 server) are correct with Remote UI.
Setting Mail Server
If the error is not resolved, check your mail server condition.
For settings and condition of your mail server, contact the administrator of mail server.
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