This list is not exhaustive.
- ASK - "Active Spam Killer" confirms the sender's email address before actual delivery takes place. A "confirmation message" is automatically sent to all "unknown" users. Once the sender replies to that message (a simple reply will do), all future emails from that person are delivered immediately. - Basically a whitelist concept.
- Black Hole | GNU Homepage - Stops spam and prevents unwanted senders from sending you email. It is put in the .qmail file and will divert spam and viruses to separate files which can be checked with an IMAP client if configured to do so. It not only uses the RBL type servers, but also checks against your own list of good/bad domains/users. You can also block email that is sent to an address that is not specified in a list of addresses to use for emailing you.
- Blackhole can log and keep the email it blocks, and can be configured to either reply with a message of your choice or make it look like you don't exist on the system. You can also add relays to the list of relays that the script skips. It also has subject line checking with ^ and $ matching lines, and includes a virus checking server program.
- blq | GNU Homepage - blq' is a script that queries various databases that list known spammers one to determine if a particular host is listed.
- SAUCE | GNU Homepage - Software Against Unsolicited Commercial Email is an SMTP front-end written to fight spam and promote good system configuration and administration. It sits between the Internet and your actual mail software. The program is extremely aggressive in checking incoming email and its sources; if it discovers any problems, it will not accept the mail. Mail from previously unknown sources is delayed to test for bait addresses or cancelled accounts. When mail is sent to a bait address its sources are blacklisted. As per the developer, the program delays mail from new sites and senders, and will bounce sites that are misconfigured, whether or not they are spam.
- Sugarplum | GNU Homepage - An automated spam-poisoner. It feeds large amounts of realistic but useless data to wandering spam-bots such as EmailSiphon, Cherry Picker, etc. This contaminates spammers' databases so much as to require culling out large portions (including any real data) and/or instructing spambots to avoid your site. -- Sugarplum detects so-called "stealth" spambots, and can activate firewalls or more aggressive countermeasures at the administrator's option. It includes Apache mod_rewrite rules for known spambots.
- HLDFilter | GNU Page - An email filter intended to replace procmail. It filters mail automatically into separate folders, and rejects unwanted mail (spam). You can auto respond with the contents of files or commands, as well as report spam to a spammer's ISP. You can also log messages, add them to a statistical Web page where you can analyze them graphically, and verify the validity of a sender's address.
- MicroSieve | GNU Page - A high speed spam filter for USENET news. Given the large amount of spam riding around in major USENET news systems, a spam filter has to be very fast and remain effective. It checks for duplicate and large articles, spambots, and binaries in non-binary groups. It also has path-based auto-accept and auto-reject, as well as cross-post limiting.
- Greylisting The SMTP protocol allows a mail exchanger to tell a machine that wants to deliver an email to try again later. Normal email servers will retry after a suitable delay when told that a temporary problem has occoured. Common spamming software never retrys. Greylisting uses this difference to avoid spam while not loosing legitamite email. This is currently very effective but if greylisting becomes commonly used the spammers will allow for it.
Spam-Filtering and Anti-Spam
- Spam Laws
- Anti spam tips - Anti spam tips and solutions
- CAUCE - The Coalition Against Unsolicited Commercial Email
- Fight Spam On The Internet!