"Ubsubscribe" from mail list does not work

I am getting pretty pissed off from periodic emails asking me to renew my PDF Architect subscription. Clicking to "Unsubscribe" seems to open a webpage saying "Success", but obviously it does not work.

On the other hand, replying to "info at send dot pdfarchitect dot org", where these emails originate from, signed by "Paul at PDF Architect", leads to nice NDR, like every spammer does:

Sorry, we were unable to deliver your message to the following address.
"info at send dot pdfarchitect dot org":
554: 5.7.1 Recipient address rejected: please use correct mailserver

I would be really nice if you guys get your stuff in order, and stop spamming.

p.p. What are these effing rules for links? I even can't put that email address here without jumping hoops...