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Spam Hammer is a method of defending e-mail users against spam by “temporarily rejecting” any email from a sender it does not recognize. If the mail is legitimate, the originating server will, after a delay, try again and if sufficient time has elapsed, the email will be accepted.

If the mail is from a spammer it will probably not be retried since a spammer goes through thousands of email addresses and typically cannot afford the time delay to retry.

What are some spamming sources?

• These are often virus infected home PCs.
• Occasionally they are infected web servers (including scripts on some servers).
• In many cases, they are a dedicated spam server with too many addresses to bother retrying. Many do retry after a few seconds (thus the +11 second requirement) when deferred.

I tried it out for a week, it is highly effective anti-spam technique. It is also called greylisting (check wikipedia)

 

Why it works

Greylisting is effective because many mass email tools used by spammers will not bother to retry a failed delivery, so the spam is never delivered. A spam sender may retry with a different sender, and possibly a different message, because it has a queue of victims rather than the proper queue of messages that regular mail servers maintain.

In addition, if a spammer does retry a delivery after the waiting period has expired, any one of a number of automated spamtraps will have had a good chance of identifying the spam source and listing both the source and the particular message in their databases. Thus, these subsequent attempts are more likely to be detected as spam by other mechanisms than they were before the greylisting delay.

Disadvantages

The biggest disadvantage of greylisting is that it destroys the near-instantaneous nature of email that users have come to expect. Mail from unrecognised senders is delayed by typically about 15 minutes, and up to four hours. A customer of a greylisting ISP can not always rely on getting every email in a pre-determined amount of time.

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Question :

I have just signed up a hosting account and setup email accounts. I wish to forward all my emails to my comcast.net email account, it doesn’t work. Any suggestions on how to fix this ?

 Answer :

Please avoid forward your emails to a comcast.net address. Forwarding doesn’t filter out any of the spam. So, the Comcast servers see a load of spam coming from your mail servers, and blacklist them. Then, none from the server can send mail to comcast.net addresses until the blacklisting gets lifted. But then, it just happens all over again.

There is absolutely no reason for forwarding email from your server. If you want to receive all your mail elsewhere then redirect the MX record. If not then simply set up your email program to retrieve from your host as well as where ever else you get mail. Most email programs can handle retrieving emails from as many millions of email accounts as you have.

Forwarding emails means that you run the risk of having the receiving account supplier misidentifying your server as a spammer source and then neither you nor anyone else with accounts on your server will be able to send mail to that email accounts with that supplier.

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The Anti-Spam SMTP Proxy (ASSP) server project is an Open Source platform-independent transparent SMTP proxy server that leverages numerous methodologies and technologies to both rigidly and adaptively identify spam. ASSP is easy to setup because it requires only minor changes to your Mail Transfer Agent (MTA).

This are part of the advantages of ASSP

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. Early Sender validation — Kills most spam before it ever reaches the server.
8. Senders receive immediate notification if mail is blocked but no erroneous bounces are ever generated.
9. Redlist keeps an address off the whitelist.
10. No-processing addresses pass through.
11. Makes use of honeypot type spambucket addresses to automatically recognize spam and update your spam database.
12. Bayesian filter intelligently classifies email into spam and non-spam.
13. Supports additional site-defined regular expressions to identify spam or non-spam email.
14. Can optionally block all non-whitelisted email (for anti-spam zelots).
15. Mime encoded and other camouflaged spam is also recognized.
16. Automatically maintains the spam and non-spam databases.
17. Accepts whitelist submissions and spam error reports by authorized email.
18. Optionally rejects executable attachments from non-whitelisted (or all) addresses.
19. Free (as in speech) software — Licensed under the GPL.
20. Practically no maintenance required.
21. Active user community and email list for support questions.
22. Source code included if you need to customize your installation.
23. Runs as a service in Windows NT / 2000.
24. Optionally blocks no mail but adds an email header and/or updates the message subject.
25. Optionally uses community-based spam statistics to identify hosts that are likely to send spam or non-spam mail.
26. In *nix environments can switch to non-root user. Also supports chroot jail.
27. Individual users can be configured to receive all mail.
28. Shows detailed analysis of spam rating process for specific messages.
29. Option to forward a copy of every rejected mail to an address.
30. Can block spam-bombs (when spammers forge your domain in the from field).
31. Keeps spam statistics for your site.
32. Detailed documentation.
33. Can listen on more than one smtp port.
34. And much more!

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