Can you please take this into consideration and allow customization of ok/error subjects, or at least mark it in the subject with a simple suffix saying " with errors". By signaling the subject when errors are found it will be easily spotted by a rule on any rules capable mail client and a corresponding alert triggered.
Another possible way could be to only email RBL reports IF blacklisting have been found.
Hope you can take into consideration as it cannot be too difficult to code and is an improvement to the product
Best regards
Marcelo