[Imap-uw] Why Postfix/local is so much faster than UW/tmail?

["Ing.BcA. Ivan Doležal"]

Hi,

    I'm currently running a mailserver in MBOX format, getting ready to 
migrate to MIX.

    Postfix is the SMTP server and it provides its "local" utility to 
deliver a mail to MBOX, which does very fast. Today, in preparation to 
switch, I changed mailbox_transport to tmail and the server died with 
load >700 during regular working day.

    Why this? Should this remarkably improve with switching to MIX?