You're on Report -- As we've noted in previous articles about spam, one method of fighting it is to report the abuse to the network on which the spammer has an account. This can sometimes be tricky to find out, but the top two Received: header lines in email are usually a good way to learn where the message originated and from where the sender had connected - these can't be forged. (In some mail programs, the headers may be out of order or reversed; in that case, look for the Received: header line that shows the email being received by your provider or company's mail server.)
I did an experiment one Sunday afternoon and reported 100 spammers back to their networks, in most cases UUNET, Netcom, PSI, and MCI. By the next week, I had received messages that most of these users' accounts had been cancelled, or their downstream ISP was informed of the spam. Several smaller ISPs whose mail servers had been hijacked had already installed relay safeguards to prevent recurrence. Sure, spammers can just open another account somewhere else or find another mailer to hijack, but there's some satisfaction in having made their lives a little more difficult. [GF]