Radically delayed email deliveries and reception?

[jols]

Hosted customers are complaining about delayed email deliveries and reception. Yes, one of our servers is pretty busy, but is a large and powerful multi-processor server. Nevertheless, upon clicking Mail Queue Manager I often see over 14,000 messages in the queue, most have been there for days, a few for as long as a whopping 120 days!!

Of course this stuff is usually just spam that has been filtered out by the MailScanner installation, and is waiting for deletion. But then many times I see that someone has sent a message, CCed it to a dozen or so people and it has been in queue for 27 days. What's going on here?

What can be done to speed up email deliveries? What can be done to make the email queing way more efficient than it is now?

[chirpy]

Response added to your other post in the same vein:
http://forums.cpanel.net/showthread.php?t=28552