
Archives of spam (a corpus, or corpora) can be useful to researchers who are developing spam filters, and can sometimes act as a source of evidence to trace a particular spammer.
SpamAssassin public mail corpus - SpamAssassin.apache.org/publiccorpus/ - spam and ham
Spam Archives (Corpora) - www.iit.demokritos.gr/skel/i-config/downloads/ - mirrors: www.aueb.gr/Users/ion/publications.html
news.admin.net-abuse.sightings - news:news.admin.net-abuse.sightings - see: Google Groups archive
nl.internet.misbruik.spam-signalering - news:nl.internet.misbruik.spam-signalering
abuse@nic.it inbox - listserv.nic.it/cgi-bin/wa?A1=ind0310&L=abuse
TREC Corpus (2005) - plg.uwaterloo.ca/~gvcormac/treccorpus/
TREC Corpus (2006) - plg.uwaterloo.ca/~gvcormac/treccorpus06/
Image Spam Dataset - www.seas.upenn.edu/~mdredze/datasets/image_spam/
Spam Archive - untroubled.org/spam/
Toasted Spam File - www.toastedspam.com/stupid/
Spam Hall of Shame - www.sput.nl/spam/spam-hall.html
Dolphinwave archive of spam reports - www.dolphinwave.org/spam/ - includes spam reports
Spam Honeypot Archive - schnarff.com/honeypot.html
Unspammable - unspammable.xtdnet.nl/
The Spam Register - www.spamreg.com/
Great Spam Archive - www.annexia.org/spam/ - no longer available - Xtdnet Spam Archive - www.xtdnet.nl/paul/spam/
Spam Received at MIT - mit.edu/network/spam/examples/
Dornbos Spam Archive - www.dornbos.com/spam01.shtml
Spam archives without headers or full source are of no practical use.
Stephen Newton's Museum of Spam - www.spammuseum.co.uk/
Lets Blog Spam - www.letsblogspam.com/
SpamAssassin public mail corpus - SpamAssassin.apache.org/publiccorpus/ - spam and ham
The Enron Corpus - www.cs.cmu.edu/~enron/
DKIM Message Corpus - testing.dkim.org/messagecorpus.html
CEAS '08 Spam Challenge — Collection Site for Email Donations - ceas.klika.eu/ceas/