PHP Mass mailer

Need to develop simple "mass mailer" script for adding to an existing PHP website. Our server is not able to handle mass emails deliver. Hence, we need a PHP program which can pull the email address from MySQL database and push to reliable host that can send emails without delay. This script should be able to talk to a reliable third party email server to send mass emails. Also, the email sending should not affect the page loading time. Feel free to suggest any commercial service providers for sending mass emails. We will subscribe to it so that the developer can use the service to integrate our website.