On 1/5/2012 10:24 AM, Eric Lemings wrote: > Well I spoke too soon. The flood of spam started again this morning. > > Obviously something isn't working. All testimonials I've read say that grey > listing stops 90% of spam but its not working. > > Eric.
How effective any particular anti-spam method is depends greatly on where you spam comes from. Greylisting is very effective against spambots delivering directly to your MX, but does nothing with spam coming from a real mail server or a trusted upstream relay. Dnsbl's likewise are very effective against known spam sources connecting directly to your MX, but will not reject mail from a trusted upstream relay. Dnsbl's might also be ineffective if your DNS source is blacklisted by the dnsbl provider. Postscreen is also very effective against bot spam and known dnsbl listed spam sources, but is ineffective if the mail passes through a trusted upstream relay. One thing you'll notice above is that the most effective anti-spam techniques are ineffective if your mail comes from a trusted relay. So you have to do some research. - are you using an upstream relay or is mail delivered direct to your postfix? - where is your spam coming from? - how does the spam get to your inbox? What servers does it typically pass through? - are your dnsbl's working? - do you need more filtering such as SpamAssassin or clamav? We can't answer most of these questions without knowing a lot more about your system and your spam -- which we might not care to spend the time doing. And of course spam evolves over time. What worked great 2 years ago might be useless now. -- Noel Jones
