Qmail problems - CPU load average rising too high
I´m running qmail in my server improved with Spam Assassin and Clam AntiVirus Daemon. I´ve realized that ocassionally the server load average rises too high. First I believed it could be related with Spam Assassin or Clam Antivirus. I´ve tried qmail running alone and then running with each one of this two services and finally with both at the same time. I´ve noticed that CPU load average rises when spam assasin was running. So I´ve decided to turn off spam assassin. Today, with spam assassin turned off, again CPU load average rises to high values and as soon as I´ve turned off qmail the load average went down.
So my questions is : Is there anyway to improved qmail performance or is there any setting that could be responsable of this behaviour of qmail? Is there anyway to prevent CPU load averages rise so high when qmail starts behaving this way?