You have sent a message from your email address "email@example.com" to "firstname.lastname@example.org (jiva adamou)".
This recipient uses Challenge/Response Spam Protection to Receive email messages only from approved/verified email addresses. This page allows you to add your email address to the recipient's list of approved email addresses.
Because spammers usually send messages from non-existing email addresses, they are unable to complete this validation process. To enter the confirmation code and click on “Validate” button is easy for people but impossible to rewrite for automated systems. This is how Challenge/Response Spam Protection effectively stops spam.