Challenge Response Spam Filters Explained by Niall Roche

As the flood of spam increases end users are looking for new and more efficient solutions to block spam. In turn software developers are knocking themselves out trying to come up with the killer app that will stop spam forever.

For several years now companies have been focusing on faster and smarter software to be installed on your PC or on your servers that will detect spam through increasingly more complex algorithms. The ingenuity behind these products can't be argued with. The problem was that as the spam filters became better so did the quality of the bulk email software used by the spammers. The battle to fight spam was spiralling out of control.

There's an old scientific principle called Occams Razor. It simply means that all things being equal the most simple solution is often the best one.

Somebody somewhere realized that there was a simple solution to the vast majority of spam. Spammers email millions of people each day. This is an automated process that they can't possibly monitor manually. Enter challenge response spam email filtering.

When using a challenge response system each email address must be authorized to deliver email to you. You can either authorize these email addresses manually by adding them to your challenge response whitelist or the challenge response email server can take care of that for you.

The process is simple but incredibly efficient.

Spammer sends email

Challenge response email server doesn't recognize address so issues a challenge email that must be phyiscally answered by a real human.

Challenge answer = yes = sender is authorized to send you email

Challenge answer = no = senders email address is added to blacklist and all future email from them is automatically blocked.

Challenge repsonse spam filters demand that a real person reply to the challenge email. Spammers who generate millions of emails a day simply don't have the time to do this and are therefore blocked from sending you any future junk email.

Using a challenge response system initially can be extra work but after 30 days you'll see a dramatic reduction in the amount of email you receive from spammers. Our challenge response system is currently showing 11,000 blocked pieces of spam in the last *5 months*. Those are hard figures to argue with.