EmailAbuse.org: Tips to help identify and report email abuse.
eMailTrackerPro: Helps identify the true source of e-mails, to help identify and report spammers. Analyzes e-mail headers and provides the IP Address of the machine that sent the e-mail.
Exterminating Spammers Step-By-Step: Describes procedures and basic tools that recipients can use to report senders of unsolicited commercial email.
JMHO on Spam: Resources for tracing and reporting spam.
Mail Parsing & Tracking: Displays visual email routing and the time taken to go from server to server, allowing each mail server hop to then be queried against common spam blacklists.
net.demon: Downloadable software to trace the sender of an e-mail and locate the spammer's real web site.
Project SpamChart: Tracks spam statistically as reported by numerous users running SpamAssassin.
Reading Email Headers: An in-depth analysis of how e-mail is sent and how to read its headers.
SpamX - Blocking, Tracking and Reporting: Effective software to help block and report the sending of spam. Works with existing POP3 email account(s) and runs on Mac or Windows computers.
Stop Spam FAQ: How to find a spammer and how to respond to spam.
The Spamhaus Project: Tracks known Spam Support Services and lists the ISPs who keep organized spamming alive; includes news, block list and ROKSO, the Register Of Known Spam Operations.