Consider using Parallel::ForkManager to fork off 10 or 20 (or more, depending on the machine and load) e-mailing processes. Check out the sample code in this node.

Also, please use Super Search. You'll find that this question has already been answered. Keep searching to learn more about valuable modules like CGI.pm (to help pull in your parameters), and Email::Valid (so you don't send e-mails to invalid e-mail addresses).