windtear 追求完美

1. Most spam has an invalid bounce address, so notifying non-delivery simply bounces to Postmaster, creating even more wasted bandwidth. Failing to notify non-delivery is a problem for false-positives. The SMTP server is the only place where spam can be stopped before entering your system.
2. The only possible feedback for spammers to void an address is from the SMTP server.
3. Spam that passes through your SMTP server into mailboxes incurs cost to your organization: storage, transmission, backup, deletion -- in all these ways spam costs you money. The only way to minimize cost is to reject it at the initial point.

However, mail transport systems are slow to adopt new technology, and spammers are quick and flexible, able to adopt new technology as quickly as it becomes available. Consequently, most SMTP servers are ill equipped to stop spam.

Furthermore, one spam-stopping solution could work with all existing SMTP servers if it was implemented on a second level -- a transparent SMTP filtering proxy. This was my goal for this project.

I wanted a server that accepted connections on port 25, passing the transmission on to the official SMTP server, and relaying its replies back to the SMTP client. But when enough of the message had been transmitted to validate its legitimacy the ASSP server could either pipe the remainder of the message to the official SMTP server or close the connection to the official SMTP server and ignore the remainder of the message.

The Anti-Spam SMTP Proxy (ASSP) Server project is an open source platform-independent SMTP Proxy server which implements whitelists and Bayesian filtering to rid the planet of the blight of unsolicited email (UCE). UCE must be stopped at the SMTP server. Anti-spam tools must be adaptive to new spam and customized for each site's mail patterns. This free, easy-to-use tool works with any mail transport and achieves these goals requiring no operator intervention after the initial setup phase.

1. Easy browser-based setup (optional).
2. Uses your existing message transport and existing SMTP server.
3. Works with Sendmail, qmail, Postfix, Imail, Exchange, Courier, Mercury, Lotus Notes, and all other standard SMTP servers.
4. Runs on Linux, Unix, Windows, OS X, OS/2, and more.
5. Automatically customizes to your site's unique email profile.
6. Automatic whitelist -- noone you email will ever be blocked.
7. Senders receive immediate notification if mail is blocked but no erroneous bounces are ever generated.
8. Redlist keeps an address off the whitelist.
9. No-processing addresses pass through.
10. Makes use of honeypot type spambucket addresses to automatically recognize spam and update your spam database.
11. Bayesian filter intelligently classifies email into spam and non-spam.
12. Supports additional site-defined regular expressions to identify spam or non-spam email.
13. Can optionally block all non-whitelisted email (for anti-spam zelots).
14. Mime encoded and other camouflaged spam is also recognized.
15. Automatically maintains the spam and non-spam databases.
16. Accepts whitelist submissions and spam error reports by authorized email.
17. Optionally rejects executable attachments from non-whitelisted (or all) addresses.
18. Free (as in speech) software -- Licensed under the GPL.
19. Practically no maintenance required.
20. Active user community and email list for support questions.
21. Source code included if you need to customize your installation.
22. Runs as a service in Windows NT / 2000.
23. Optionally blocks no mail but adds an email header and/or updates the message subject.
24. Optionally uses community-based spam statistics to identify hosts that are likely to send spam or non-spam mail.
25. In *nix environments can switch to non-root user. Also supports chroot jail.
26. Individual users can be configured to receive all mail.
27. Shows detailed analysis of spam rating process for specific messages.
28. Option to forward a copy of every rejected mail to an address.
29. No perl modules to install -- runs complete "out of the box".
30. Can block spam-bombs (when spammers forge your domain in the from field).
31. Keeps spam statistics for your site.
32. Detailed up-to-date documentation.
33. Can listen on more than one smtp port.
34. And much more!