Canon MB2100 Series Online Manual page 1034

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Cause
Communication with mail server failed.
What to Do
Press the printer's OK button.
Make sure that the APOP authentication settings of your mail server and printer are match.
For printer's APOP authentication setting, use Remote UI.
Setting Mail Server
If the error is not resolved, check your mail server condition.
For APOP authentication setting of your mail server, contact the administrator of mail server.
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