> What happens if I dont comply? >You get marked as spam? And that's probably the best case scenario. Your email may not get delivered. My best friend works at a large ISP specifically on their email transport system. They discard 97% of the emails they receive. That's straight into the bit bucket, not to your Junk Mail folder.
Really infuriating, because customers would not believe that this wasn't a problem on our end, it was the other side telling us to discard their email!