Or create a mail filter that scans for the offending addresses and send them to a mail purgatory folder. Do whatever you feel is an appropriate response to the spammer's discourteousness. Two other good tools are nslookup and whois. Nslookup is useful for finding the DNS names of IP addresses that initiate the spam. Once you know the domain, perform a whois search to get the contact information.
Whois searches provide the administrative and technical contacts for the domain.
In addition, you can also tell who the provider is for virtual domains. Too many spammers have figured out how to forge their domain name by entering a fake domain in their network preferences. Forging the IP address requires a bit more skill. Once I get a valid domain, I usually forward the spam to the contact addresses provided by whois. This Week's Question.