In the section Settings> Organization (point 5: e-NOTUM activity) you can define an e-mail address in the field: Error warning e-mail.

Errors that occur in the notification lifecycle (could not be registered or deposited or expired) will be sent to this mailbox, as well as errors in sending status changes to integrated applications (if applicable).

This mailbox is customizable. If no specific address is set, by default, e-NOTUM sets it to be the same address to which the daily reports are sent.