1One of the approaches used to identify spam goes like this; if I see a spam message at 8:30 in the morning, I send a checksum of that message to an online database of spam. When you get that message a little later on in the morning, your mail system asks that online database, "Has anyone reported this as spam?". The online database can report back "yes", allowing your mail system to raise the spam score for that message.
SpamAssassin has support for three different NetworkTests.
- The Razor database (http://razor.sourceforge.net) Vipul Ved Prakash and Jordan Ritter allow Unix clients to work out of the same database used by the commercial customers of the Cloudmark system. See UsingRazor for help on using Razor.
- Pyzor, a completely free database and software system, written by Frank Tobin. http://pyzor.sourceforge.net
- DCC, the Distributed Checksum Clearinghouse. http://www.rhyolite.com/anti-spam/dcc/ . See UsingDcc for help with DCC issues.
Note that these all require access to their servers through your firewall, if you have one. Read NetTestFirewallIssues for details.
DnsBlocklists can be queried via the network, so these are network tests too – but they get their own page.