Today I learned something new. A customer called in that she was not receiving her emails from us. When i checked in Postmark it did show that it stopped working it was a 'Hard Bounce'. Next to the first occurrence was a 'Reactivate' button. I clicked that and  voila! instant success.

I learned that the 'Reactivate' is an available option as long as they have not marked us as 'Spam' on their end. It isn't retro active, but from that point on it will start sending again. :) I had her Test it out and it worked wonderfully.
Just FYI.