At our company we kept getting emails from them on email addresses that are only used to send data to our service. This was starting to become a problem, so we called them up and asked them to block that domain. They said no. Eventually they said they'd blacklist the email addresses individually. Our response was "OK so we're going to send about 20,000 email addresses for you to blacklist, and probably about 1,000 more every 2 months or so". They blacklisted our domain.