apt confusion

[Alex Dean]

I want to remove the exim4 MTA so I can install qMail.  There seem to be 
some connections between packages that I don't understand, because every 
time I try to remove exim, it also removes MySQL, PostGres and a few 
others...

    # apt-get remove exim4-daemon-heavy
    Reading Package Lists... Done
    Building Dependency Tree... Done
    The following packages will be REMOVED:
      at courier-pop exim4-daemon-heavy mailman mailx mutt mysql-server-4.1
      postgresql postgresql-contrib

This doesn't make any sense to me.  Why can't I just remove exim?

I thought 'OK, maybe I just have to remove it all for some reason, and 
then I can later re-install MySQL'.  But, when I do that, it also 
reinstalls exim!

    # apt-get install mysql-server-4.1
    Reading Package Lists... Done
    Building Dependency Tree... Done
    The following extra packages will be installed:
      exim4 exim4-daemon-light mailx
    The following NEW packages will be installed:
      exim4 exim4-daemon-light mailx mysql-server-4.1

Anyone have any ideas what's going on here?  
http://packages.debian.org/stable/mail/exim4-daemon-heavy shows that 
'exim4-daemon-heavy' depends on 'libmysqlclient12', which in turn 
depends on other MySQL packages, so I can see how installing exim might 
require MySQL.  But I don't see why installing MySQL requires exim.  
Additionally, that's just 'exim4-daemon-heavy'.  When I just 
re-installed MySQL, apt installed 'exim4-daemon-light', which doesn't 
seem to have any MySQL dependencies.

thanks,
alex