Challenge and response email services claim to clear your email inbox from spam. Logically, all legitimate senders have to confirm that they indeed sent an email to you before the email goes to inbox. Usually, the sender has to do it once.

For email marketers, the system pose a problem. As more and more people use it, there is no choice but to manually respond and confirm to the challenge to have future mailings go through the recipients’ inboxes.

You need to either draw a hard line or invest the staff time to deal with challenge/response.

Fortunately, the concerns about spending a lot of time to respond to challenge/response confirmation emails never happen. In fact, the percentage of users using the system is fairly low. The usage is not increasing too.

According to Al Iverson, Exact Target’s Director Privacy and Deliverability:

“Your bank, your online travel site, that online store you recently bought DVDs from; very few of these very legitimate senders have the resources or capability to respond to C/R requests. You’ll find that most of them silently discard replies, as they come back mixed in with tons of spam, viruses, blowback, out of office replies, etc. I think after suddenly not receiving mail they want, users often rethink their use of C/R.

“Also, C/R can be a significant technical hurdle to overcome for novice e-mail users. Let’s say that some father e-mails his son and receives a C/R reply. Is he going to be tech-savvy enough to understand what’s going on? The experiences I’ve had don’t make me confident that this is the case.”

[Email Insider]