Dumbster is very useful, but it has been a tough time for me to make it work with multiple line headers, in particular "To". Vanilla dumbster does not have support for that, so I am unable to check in my unit tests if the "To" header is correct.
If you have similar problems, check this patch that is over an year old.
But also read the comment I wrote about a potential bug in this patch. Replace the code I mention in the comment if it is also your case.