Canon PRO-6000 Online Manual page 784

3421
Cause
Communication with mail server failed.
What to Do
Tap OK on the touch screen to dismiss the error.
Check that the receiving account and password are correctly configured in the RemoteUI mail server
settings.
Setting Mail Server
If this does not resolve the error, check the status of the mail server.
Contact the mail server administrator to check the server settings and status.
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