Canon imagePROGRAF GP-4000 - Manual (Page 932)

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Cause
Communication with mail server failed.
What to Do
Tap OK on the touch screen to dismiss the error.
Check that the settings on the mail server and the APOP settings on this device match.
Check this device's APOP settings in Remote UI .
Setting Mail Server
Contact the mail server administrator for configuring APOP on the mail server.
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