Here's how to apply the qmail "bigext-todo" (to prevent "silly qmail syndrome") and "outgoingip" patches (set IP in /var/qmail/control/outgoingip) as well as further split the queue folders for better performance with large #s of messages in queue.
# shutdown qmail
service qmail stop
killall qmail-remote
# make sure no more qmail processes
ps auxw | grep qmail
# get and compile patches with my super-easy script
cd /usr/src
wget
http://lmhost.com/mf-qmail.tgztar xzf mf-qmail.tgz
cd mf-qmail
./cmd 8 199 #(Plesk 8.x)
cd qmail-1.03
make setup check
cd ..
./queue_repair.py -r
Next, follow the maillog while sending a test message to make sure things are working.
tail -f /usr/local/psa/var/log/maillog
Ctrl-C exits
Also contained in the archive is a script "iprotate.php" that can be run to rotate email through all IPs on the server every X seconds. The benefits of this are overrated, I believe. (If you do it make sure you have proper reverse PTR entries for all IPs or set them in the excludes() array in the script)
Regards