Question : How to test an email address for validity

I need to test a number of email addresses for validity and would like to know to do it.  I know that I can ping the domain part of the address, but I also need to verify the recipient exists.  This all has to be done WITHOUT sending actaul mail to the recipient, and hopefully without much interference with the relevant ISP.  Any existing samples or solutions appreciated.

Answer : How to test an email address for validity

NTIVER,

Yes, it stops the mail because the script does not contain the subject nor the body.  After the last verification the script returns valid on not valid cancelling the mail.