Mail_Queue problem

Hello Everyone, I am a new user of PEAR and I love the concept of the Mail_Queue for mailing out our newsletters to thousands of subscribers. I have gotten to the point where everything seems to be installed properly. When I ran a "$mail_queue->sendMailsInQueue();" call in my script to send out all mails in the queue, it worked for a while, and then hung. I am using an SMTP server to send out the emails. I thought it was stalling because it was opening up too many connections to the SMTP server, but after shutting down the database for a day and getting back to it, it still will not send out the rest of the emails in the queue. It may send out around 20 - 50 emails occasionally, but then it stops working. Does anyone know what I should check to try and fix this problem? Thanks, Tyrone