SysAdmin has an article online by some of the top technical people at Lyris (remember Lyris?): Title: Which OS is Fastest for High-Performance Network Applications? http://www.sysadminmag.com/newsletters/feature/ They use their MTA as a comparison tool, and crank it up to the equvalent of a concurrencyremote of 3000, though they don't seem to get much of a performance boost past 1000 on the hardware they're using. One of their conclusions is that their asynch multi-threaded software model outperforms the process based model which qmail uses. Is their methodology convincing? Well... However, and interesting read. John White