[support] Block users with invalid email

Dear drupal users, I have a site with some 1000 users which is now up for a very long time. I want to clean-up the user database and delete (or block) all users with an invalid email. For this I thought about a script that connects to the mail server of the entered email address and check with a MAIL FROM/RCPT TO if the email address is valid. In case it is not, block or delete the user. Before I now start to hack a little script for this, is there maybe already something available, I can use? Thanks, Matthias -- "Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the universe trying to produce bigger and better idiots. So far, the universe is winning." -- Rich Cook