Apr 25, 2006

Challenge-response spam filters


Whenever you send an email newsletter or promotional campaign, you get all kinds of bouncebacks.

That’s why it’s really important to use a reply-to email address that a human in your company actually checks on a regular basis. Especially the few minutes immediately after clicking "Send."

We just sent our MailChimp Newsletter, and within 10 seconds got half a dozen "I’m on vacation replies."

But mixed in with those autoresponders, we always find one or two "challenge-response" spam filter replies. If you’re new to email marketing, and you’re not familiar with challenge-response spam filters, read on…

Here’s how challenge-response systems work.

You send someone an email. His spam filter says, "Hmmm, I don’t recognize you." The spam filter sends you back a reply with some kind of question, like "how many puppies do you see?"


If you answer correctly, it proves you’re a human (and not some kind of spam-bot), and you’re added to the recipient’s "approved" list. Once you’re on the list, you never have to do it again.


Here’s some information about one popular challenge-response system, MailFrontier Desktop.

There are other challenge-response systems that require you to answer a question, but then they also give you an opportunity to send a brief message to the recipient, so he’ll be reminded of who you are (Earthlink uses this approach). For example, I once met with a potential client, then sent a followup email after the meeting to thank him for his time. I got an Earthlink challenge-response email, asking me to provide a little explanation of who I am.

So you really can’t just blast out a campaign and walk away. Make someone responsible for checking the bounces, and be sure to tell them how to respond whenever they get a challenge-response email.