It is very important that Click2Sell only sends mail to ‘reputable’ email addresses. We use validation to review every email that is put into our system and it must score a high enough score to allow us to send an email. This is to protect our sending reputation as well as all of our customer's sending reputation.
If your email address(es) failed validation it means that the score is too risky to send to. It does not mean that the email is not a good or valid address it just means that this address has proven to be risky in the past. This can happen because the user reports “fair” emails as Spam or because their email inbox is often full. Many things can cause this. We evaluate emails as they are entered into our system and recheck them from time to time and adjust accordingly based on any change in scoring.