We're having difficulties sending out our newsletters with qmail on plesk 7.5.x. We've tried just about everything from setting an ultra high concurency remote to disabling all antivirus and spam tools. We have a few newsletter lists some of which can be up to 150k emails in size. We send personalized emails and from what I've read, qmail seems to have a problem when you inject a ton of emails. Generally we're seeing very low remote concurency, even though its set at 250 it rarely reaches 50 and generally hangs around 10. The problem generally manefests its self in high iowait (50-75%) and little if none system or user processor usage (1-2%). Our email scripts seem to spool quickly to qmail, at which point they take quite a long time to preprocess and eventually begin sending. I'm curious what others have experienced and if anyone has any suggestions. I may try installing a barebones linux install and toss a DNS server and Qmail on it to see if I can compare the speed between a barebones qmail install and a plesk qmail install. The main reason I think there is somthing fundementally wrong is that some of the benchmarks I've seen of qmail seem to indicate that it should be performing much faster. I'm currently running RHEL 3, Plesk 7.5, Dual Xeon 3.2, 2GB Mem, SCSI Disks.