Logged in to the Registrar web, you as the registrar can choose to subscribe to errors in the DNS regarding the domains that you manage as a registrar. The tool that tests the domains and sends out an email is called Zonemaster. You can read more about Zonemaster here.
These emails contain an overview, including an attached more detailed description, over domains in the .se and .nu zone that Zonemaster considers have persistent problems. Every day, at a time when few changes occur, Zonemaster goes through all tests run over the last 24 hours and builds an email per registrar with domains they manage that generate serious errors that haven't been fixed. This email will then be sent to the email address you have entered for this purpose.
This service should be seen as a tool to simplify problem handling with your customers. At most one email per day will be sent and, hopefully, you will quite often not get one at all. Also, considering this email is based on live changes in the zones and also on time (only the last 24 hours are considered), you will not get any duplicates or other unnecessary information in these emails.