I would be looking at something in your DNS that is not configured
correctly - ie; typo, bad cname, etc. To start from scratch on DNS, make a
copy of your /etc/named/records file and remove the original file. You will
need to click on "Save DNS Settings" in control panel to allow DNS to start
from scratch. At this point take a look at DNS and see if it appears to be
running correctly e.g. low cpu, etc. If everything seems fine start
entering
(via the gui) some DNS entries for websites and see if sendmail works OR if
it pukes out. This will at least point you in which direction to go in;