I believe for the most part every directory owner requires a functioning email accompany every submission. But, how do you handle when the submittor used an email that requires verification prior to accepting an email? I got one today where the original "Thank you for submitting" email bounced back and I was instructed to send the email again with the crazy heading that the 'failure' notice had. I had been leaning towards deleting the entry for other reasons anyway, so this just made the decision easier. But I was just wondering, do you take the time to play this game or do you consider this an "invalid" email and delete submissions that use an email like this?
for free directories, I would suggest that you reject the sites with invalid email id's. This is one way to keep the 'intelligent' submitters away