From AutoSPF

Many people consider the problem of spamming to be some kind of invincible nature disaster. A phenomenon which, though may be whithstanded more or less efficiently, can not be liquidated. The reason is that today there are no any "standard" techniques of email filtration. The same letter may be regarded as spam by one user and as not spam by another. Nevertheless, spam problem is not unsolvable. Even today in many countries legislative mechanisms offer the possibility to go to law against a spammer and his client, and claim moral and material damages. Unfortunately, SMTP mail transfer protocol being in use today does not always allow to identify real message sender with responsable accuracy. The method we offer consists in analysing the possibility of identifying real message sender under the existing SMTP protocol. A letter is considered trustworthy if actual sender is known or can be detected easily. On the basis of the idea we have designed AutoSPF, an efficient message sender verification system, and SMC-milter, junk mailing (spam) protection system implemented in the form of plug-in for milter API supporting popular message transfer agents (MTA).

Please note the fallowing! You can check the work of AutoSPF algorithm using the form on the right. As source data there are used host part of sender address indicated in "From:" header (e.g. mail.ru) and sender's IP address, indicated in the brackets in the first "Received:" header record (e.g. 194.67.57.229). In order to see mail headerss, open "Source Message Code" in your e-mail program.