Assuming the entry in the field I put firstname.lastname@example.org is an address you have tested sending an email to you can filter out any relay quirks.
Then you have the send notice, obviously if it is set to a regular interval you can go through the printers fault history, find the faults at the specific time + or - 5 minutes to diagnose an actual error. And make sure the printer knows the time and date correctly.
If it is on Immediate notice just casue an error , wait 5 minutes and check the fault history.
Failing that, the printers account may have triggered the SMTP server to block the alerts due to frequency (Somebody opened the tray 5 times in 3 minutes) or the subject line since it never changes (same email sent constantly), Hosts like Gmail and Office365 both will block them server side.