Ok, here's my situation. I have a P4 2.4GHz running qmail. I recently sent out a LOT of email (no not spam, for dynamic mailing lists) the mail send went well, however each time qmail dumps the remaining not sent mail out of the queue, the box starts timing out incoming connections. This box is behind a Linksys RV-082 10/100 VPN router (VPN not being used) the connection to the world is 100 megs and the ethernet card in the box is a 1 gig. top shows cpu usage ~ 3% during all this. The procs do head up around 200. I'm not sure why the entire box slows down (internet wise) when the qmail queue is dumping. MRTG shows that I'm no where near my 100 meg pipe limit. The load average on the box also stays very low around 0.50 - 0.15. I also have another box behind this router which is effected by the slowdown as well. This leads me to believe it's the router.

I could only take a guess at the cause but it could be a dns issue. Do you have both machines sending dns requests to the router.

Try setting your second (non qmail) PC up to use an external public dns server (no the one your router uses) and see if that speeds things up.

That makes a lot of sense, I use external DNS servers for both machines. However the email machine was only set to use one DNS server, which was the other machines primary. I added the other DNS server and made it's primary the other systems secondary. Thanks for the help, I hope that fixes things. If you think of anything else please let me know