The Challenge And Response Spam Filter
Spam Filtering Techniques
There have been many different anti spam technologies used by different applications in order to try to prevent or minimize the occurrence of spam that users receive. Some proved initially effective but the perpetrators of these irritating emails eventually found a way around them. Some applications use a strong concoction of several different techniques combining them to essentially generate an impregnable line of defense. However, one area of spam prevention that remains almost entirely effective is a challenge and response spam filter. While it is entirely bullet proof, in so far as you will not receive spam emails when using one, it is also considered by a lot of users to be too much trouble to use.
What Is A Challenge And Response Spam Filter?
A challenge and response spam filter works on the premise that spam emailers are non responsive. Usually spamming is done using a mass emailing system and this usually means that the email address is either hidden for the protection of the spammer, or is unchecked by humans. In either case the chances of receiving a response from that email address are slim at best. When your email server receives an email from an unknown sender's address it will send a challenge email. Until it receives the desired response the email will be blocked from being downloaded to your email client.
Introducing The Challenge Email
A challenge email is a polite and typically unobtrusive email asking the sender to verify that they are a genuine user. Verification, or response, is done by clicking a link within that email. Once the link is clicked the challenge and response spam filter recognizes that there really is a human on the other end of the email and forwards the outstanding email to your desired email client. The email address of the sender is also added to a whitelist in order that they can email you again without having to go through the challenge and response process again.
What Happens To The Spam Email
When you receive a spam email the challenge email is still sent but nobody will click on the response link. In this case the sender is never placed on the whitelist and no emails, including the original one, from that sender will be allowed to pass through to your email client. As such a challenge and response filter is a guaranteed wall against the numerous spam emails that many of us receive on a daily basis. However, it does have a problem.
Potential Loss Of Important And Genuine Emails
Most users will not have a problem with quickly clicking a link in an email in order to enable emails to be sent to your email client. However, if you use a challenge and response filter on a query email address for your business or website you may experience a slight dip in the number of people that actually contact you. From your point of view you will not notice a difference in your emailing habits. You are not prevented from emailing other people and you will still receive the genuine emails that are sent by genuine people. You may need to manually add some email addresses to the filter's whitelist though.
Manually Adding Senders To Your Whitelist
Because emails can not be delivered until the sender is on your whitelist this means that automated, but still genuine, emails may be blocked. When you purchase items online, for example, you may receive an invoice or a receipt for your goods that includes important tracking information. If you do not place the email address of the automated email in your whitelist you will not receive the email without manually searching for it.
Is A Challenge And Response Filter Right For You?
A challenge and response filter is one of the most robust and bullet proof methods of blocking spam emails from reaching your desktop. While they are unobtrusive to the user they can be considered a nuisance by some genuine senders. The final decision will mean that you need to weigh up the positives of receiving very little or no spam with the negatives of potentially missing out on valid emails (although this is not a definite).