Zenon Panoussis wrote:

I would hazard a guess that you have either ran out of pre-configured available threads for esmtpd to listen on (in which case increasing the limits will help) or your system has run out of available resources to provide esmtpd with new threads. Its the only logical reason why esmtpd can't answer requests.

Either way, since your enemy's response will be to increase the load to find your new break point, in my opinion, you need to consider clustering esmtpd, which isn't difficult if you have some spare hardware given the modular nature of courier. You'll get a load balancer project from freshmeat which you can run to delegate the esmtpd load across multiple servers. Perhaps scrambling a solution to show this guy that you've beaten him will cause him to backoff allowing you to put a more structured system in place.

Best of luck!

-Enda.