I'm sorry, I must have missed this the first time around. You said all your incoming mail goes through Quantico first, but based on the fact that they are having you mess with your equipment, I'm assuming the high queue being refered to is your outgoing, which I'll make the temporary assumption will most likely be SMTP.
The first thought that comes to mind, and the most likely thing that is happening, is that somone is spoofing using your SMTP server. Don't rule this one out. The programmer that works with me at the moment said that one of their clients is a Presbyterian church was being used for spoofing and it was so bad that they were blacklisted and could completely not send or receive emails. They had to determine where it was coming from and stop it, then prove to the ISP that it was not them, but rather spoofing, before they could get removed from the blacklist. I've never had to deal with that, so at the moment I have no way of telling you how to approach it. Starting and stopping your services or rebooting, would of course, temporarily stop the activity, because the remote connection would obviously temporarily be broken until it could be reestablished.
The second thing that comes to my mind (and not out of the question) wouldn't even be hardware at all, but rather one of your servers / clients has a virus which may be using it's own SMTP server to route it's own variation of emails. The first thing that I would do prior to investing in new equipment is to run thorough scans, including spyware and adware scans to ensure that none of your machines have an infection.
I use Symantec Enterprise and can monitor virus activity via the Control Panel. On Friday, I was applying all the recent patches from Microsoft. While doing so, I was looking up a client station IP address on the Control Panel, and not seeing his workstation listed, went to turn on his computer, but it was already on. I noticed his antivirus was disabled and no longer managed by the server. I reinabled the management control and ran a full scan remotely and discovered and deleted 135 virus infected files, primarily MyDoom!Gen (although there were others). As best as I can determine, he contracted this June 16 by visiting a malicious site. I had overlooked it for two months because I just never noticed he was no longer showing up on the management console. So again don't rule that out as a possibility. (I thought we were completely virus free, and was obviously embarassed to discover we weren't).
I would research both of those possibilities before investing in new hardware.
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