When you manage Postfix and have a trouble with your mail infrastructure, you may want to set in maintenance your Postfix without loosing any mails. Here is a way to hold the queue, giving the time to analyze the problem and then release the queue. I’ve wrote some tips on it. I hope it will help you.
When you have a huge amount of mail to deliver, you can’t release the queue at once and let the server maximize the outgoing mail throughput ! The result will be: you’ll get blacklisted from a lot of MX servers. That’s why you should take care of it and do traffic shaping. I’ve wrote a little tips on it.