This Perl module provides routines for checking validity of email address.

It makes several checks:

   1. It checks the syntax of an email address.
   2. It checks if there any MX records or A records for the domain part of
      the email address.
   3. It tries to connect to an email server directly via SMTP to check if
      mailbox is valid. It uses a combination of MAIL and RCPT commands which
      simulates sending an email. It can detect bad mailboxes in many cases.

WWW: http://search.cpan.org/dist/Mail-CheckUser/