sfsw tech newsletter

Spam Filters and POSTE

Before we could release of POSTE - Ecomgroup's new Email marketing product - research into email rejection was required. When an email is received, it may have been handed between machines on the internet - suprisingly more so that one may expect. A single email may be relayed by dozens of machines, each of which may add or remove meta-information and contribute to the eventual email that is delivered. There are two or more parts to every email. A "header" is that part that the machine understands, and the "content" is the part that we understand. The content should never be edited or touched by email forwarders as that would rather defeat the purpose of email. The content, like passengers in a taxi that has to sometimes drive through dangerous territory must be delivered as safely and as efficiently as possible. Remember, your precious piece of communication is in a forest of communication, surrounded by millions of messages carried by illegal, sometimes criminal, unlicenced or plain dangerous vehicles.

Spam filters were invented to notice patterns that tend to be used in spamming and thus filter out the content, usually without looking at the content. As a last resort, the spam filter will evaluate the content but most spam is detected in the "magic" header. What kind of things are checked? The first thing to check for is: does this mail originate from the server it claims is sending it? Another thing that can be instantly checked in a technique known as "blacklisting" is: has this mail been delivered via a known spam source? The header reveals the path that the email has traversed and one of the evolving strategies is to spoof a "trusted" source. Spam gateways check the actual source against the claimed source. If they do not match, these days, we tend to assume something is wrong and fail delivery.

Spam filters are not an exact science. They will examine the email for keyword patterns and check the status of the originating domain and not deliver mail that scores over a threashold on certain tests. We had to build a clean delivery mechanism so that email from POSTE looks like regular email and thus gets past most spam filters. The correct strategy is to follow the rules. Then the mail tends to get through. The other strategy is to continue to evolve.

POSTE is a new product by Ecomgroup Ltd. See their website: wwww.ecomgroup.biz

posted by Unknown @ 2:29 PM