Spamming?

I ran / owned a hosting company. One of our server clients used their dedi as an email server to contact people with similar domains via WHOIS. Although I am not looking to do this, I'm wondering how successful that is as a strategy and whether you would simply end up blacklisting your ips (my understanding of anti-spam laws is that WHOIS is public information and as long as you aren't harvesting addresses, you are not spamming).