Despite the amount of time that they have now been around, challenge/response systems — anti-spam programs which
quarantine rather than deliver the email you send to your intended recipient unless you are either listed on their
whitelist, or answer a challenge email (hence the name) — still seem to cause more problems than they solve.
Leading challenge/response implementation system Mailblocks, despite being one of the major players in the space,
still finds that its challenge emails end up in the spam folder at such places as Earthlink and AOL. This of
course means that the sender never sees the challenge, and so never responds, and their email is never delivered.
This is especially ironic given that Mailblocks was actually purchased by AOL in August.
Said an AOL spokesman, "We had to relist the IP addresses that Mailblocks is using to send challenges."
