I have StealthMTA setup with 1 main server and 1 cluster with 4 IPs. When I send emails the queue is always growing and never decrease. Even if I stop sending in Interspire the queue stays there for 3-4 days. The only solution I have is to clear the queue before it reaches 10,000 and resume sending. But this way I can't leave the sending on its own and have to always interfere. I suppose those messages in the queue get never sent. If you know how to fix this bug in StealthMTA please contact me through PM or post here.