Hmm, I am not so certain that this would work. You could have an active mail server but the account could be bogus. In getting the bounce backs aren't you checking the email address at that time? Wouldn't this be the same as enlisting a separate app to do this?

Some email servers are not on-line 24/7. For instance, Pharmacia pharmaceutical company shuts down access to its servers on weekends to help security. A server that is down for maintenance will bounce email sent.

You already have a system that works. Just build a script that automatically removes the email from your distribution lists if it bounces back to you.

This sounds like a way of creating Spam. A computer could sequentially generate email pings and find every useable email address unknown. What a mess that would be. I already recieve over 100 spam messages a day in my Yahoo bulk mail; I don't need more.

As someone who has set up a mailserver, this is a very bad idea. You don't want to validate email addresses. You want to make sure that the person sending the email has absolute certainty that the email they are sending exists.

Spam is a vast majority of the email sent in a given day. Thus, no matter how useful, spam must be the first and foremost consideation of any email feature.

Internal/intranet websites can use LDAP or a similar (active directory, groupwise) system to validate email and provide an employee directory if one requires.