Mon, 20 Nov 2006 12:44:16 +0000
greylist, mail, spam, spf, tech

Dropping some spam.

I have been slowly trying out new things for reducing spam. A while ago I added ?greylisting to my server so that if I did not know who you where you would have to go away and try again in 15 mins. This works pretty well but is not very user friendly so I have been extending things a little.

Helo filtering. When mail servers talk to each other the start with a nice polite hello or at least they should. I now check that this "helo" statement is correct in various ways and if not reject it. As a lot of spammers have simple bots that just try to send email without much care for protocol then this is a low cost option to cut down the cruft.

I have also turned on SPF checking so that if you have a SPF entry in your DNS I will only accept mails from your domain if they come from the servers you have listed. Lets hope that these cut things down a bit.

I may not keep greylists on forever as they do add a large delay for the first time that a user sends a mail. Perhaps I will look into accepting mails from anybody who has a correct SPF record.