i concur, sending 22k an hour isn't very interesting nor difficult. I think the highest i've tuned a system to was about 1m per hour sustained for days and this was back in 02-03 era. we definitely burned out a few parts and upset the hands in the datacenter a few times. would be a fun project to do with modern hardware, but i have no reason to send that quantity of email anymore. removing atime was probably the biggest single speed gain, along with understanding the MTA very well.