I recently upgraded my Qmail systems. Since Inter7 was the one who did it for me previously, I contracted them to do it. Two years ago I was very impressed, my load was a high 20s, after they finished it was in its low 4-5 with 4 CPU processors.
This time I asked for an upgrade for the Qmail in general and also its spam filters as I am getting more and more spams and the load is increasing. They stabilise the server loads, add tons of fantastic new layers of spamming protection, helped monitored and customised their scripts to my systems.
Real professionals and real knowledgeable people when it comes to Qmail. I had nothing but praises two years ago. Two years now, I have still nothing but praises.