Hey dude it is clear you have running exim4, remove it or stop it.
To stop it and remove it from the rc2.d:
# /etc/init.d/exim4 stop
# rm /etc/rc2.d/*exim*
To remove it just run:
# aptitude --purge remove exim4
Which reason you would have exim4 if zimbra does that job?
Zimbra use postfix Already, you need to dump exim4, it is garbage