Step 1. Send an email to the following addresses at the domain that the email originated from:
abuse
postmaster
root
sysadmin
In otherwords, let's assume the fictional domain of "stupid-spammers.com". You get an email from someone, and their address is "stupid-idiot@stupid-spammers.com". You need to send the email to the addresses I showed to you above at the domain "@stupid-spammers.com".
By using my example, let's say you want to take actions against "stupid-idiot@stupid-spammers.com" and you want to make sure those addresses I gave you get a copy of the message. Let's just use "postmaster" as the example. Send an email to "postmaster@stupid-spammers.com". See how it works?
Most organizations will have the "postmaster", "abuse" and "sysadmin" accounts. Don't be suprised if some of these accounts get returned to you as as "unknown user". This is normal. Hopefully one of these will find someone to take administrative action against that unwanted spammer.
Be aware that many spammers are setting up their own domain. It has become necessary to track down their service providers and contact the administration of those networks.
PLEASE make sure you include FULL headers and include that in the email you send, otherwise, the folks in charge of handling discipline will have a valid excuse to ignore your cry for help. The headers will show if the message is forged, or if it in fact did come from their domain.
Step 2. If you have telnet access, or even better, a shell account(where you have a text-based interface), try this at your prompt:
whois (the domain you are checking out)
EXAMPLE: Again, we'll use the domain "stupid-spammers.com"
whois stupid-spammers.com
Send email to that administrative and technical contact that shows up in the whois result. Also, you might discover that this domain is being hosted by another organization. You will usually find this from the technical and administrative contacts. Do a "whois" lookup on those domains, and send email to those technical and administrative contacts as well.
Again, include FULL headers and include that in the email you send, otherwise, the folks in charge of handling discipline will have a valid excuse to ignore your cry for help. The headers will show if the message is forged, or if it in fact did come from their domain. While you're including those headers, you may be able to find out where to actually send email to for discipline. Mainly, you may be able to find where the spam originated from, in the case of some forgeries.
Step 2 is "advanced" and not all of you will be able to do this. Don't worry, hopefully Step 1 is all you'll need to end spam from the idiot who spammed you, or posted spam.
But what if I'm being spammed from some jerk from a commercial service?
Don't fret. Through my unfortunate adventures in being spammed, I've discovered many contacts to forward this spam to so their accounts can be terminated.
Please keep in mind that this is only a partial list, so please keep me informed of contacts at other services.