In v15, if you go to Settings > Email > Notifications and check this box: Trunk/Provider responds to Request with an Error code you will get an email on each "error code" coming back from your trunk. The problem is that these are response codes, not error codes, so you will wind up getting an email every time someone in the office misdials a number (484 Address Incomplete) or gets a busy signal (486 Busy Here), for example. Of course, you could completely disable this check, but then you might miss real errors like 401 Unauthorized because someone changed your password. Because of the inconsistencies in how trunks and providers assign SIP response codes, I wouldn't want or expect 3CX to figure out which are good and which are bad. However I would like to have the option to ignore/filter out codes that I know are causing unnecessary noise in any given installation. This could be as simple as a field where I can enter a list of unwanted codes, perhaps with "?" wildcards representing any digit: Ignore SIP Response Codes: 402, 404, 48?