How Do Spammers Get People's Email Addresses?

There are many ways in which spammers can get your email address. The ones I know of are :

1. From posts to UseNet with your email address.
2. From mailing lists.
3. From web pages.
4. From various web and paper forms.
5. Via an Ident daemon.
6. From a web browser.
7. From IRC and chat rooms.
8. From finger daemons.
9. AOL profiles.
10. From domain contact points.
11. By guessing & cleaning.
12. From white & yellow pages.
13. By having access to the same computer.
14. From a previous owner of the email address.
15. Using social engineering.
16. Buying lists from others.
17. By hacking into sites.

If your address was harvested and you get spammed, the following pages could assist you in tracking the spammer down :

1. MindSpring's page explaining how to get an email's headers http://help.mindspring.com/features/emailheaders/extended.htm
2. The spam FAQ, maintained by Ken Hollis. http://digital.net/~gandalf/spamfaq.html http://www.cs.ruu.nl/wais/html/na-dir/net-abuse-faq/spam-faq.html
3. The Reporting Spam page, an excellent resource. http://www.ao.net/waytosuccess/
4. Reading Mail headers. http://www.stopspam.org/email/headers/headers.html
5. Julian Haight's Spam Cop page. http://spamcop.net/

Source: http://www.faqs.org/faqs/net-abuse-faq/harvest/