This page explains the special functionality in the class.
If the setting ApiExceptionHandling in the config file have been set to TRUE, and the returned answer form teh Integration Api is not an 200-OK, then the service will throw an exception, causing the corresponding client to try to resend the message at a later time.
However, as some of the functionality in the integration api have been rushed a bit, some returned errors are creaeted in such a way that they can be recognized from the WCF Service.
The flow in the WCF Service is as follows:

If new exceptions are to be ignored, simply add the starting number to the dictionary above and a describtion.
The error codes should start with 9000 numbers for good practice, and are determined in the integration api.