broken packages?

[Székelyi Szabolcs <szekelyi.szabolcs@kfki-lnx.hu>]

Hi,

I have a package called morg-mailcommands that depends on Postfix.
Trying to install it with aptitude gives 

> E: Unable to correct problems, you have held broken packages.
> E: Unable to correct dependencies, some packages cannot be installed
> E: Unable to resolve some dependencies!
> Some packages had unmet dependencies.  This may mean that you have
> requested an impossible situation or if you are using the unstable
> distribution that some required packages have not yet been created
> or been moved out of Incoming.
> 
> The following packages have unmet dependencies:
>   morg-mailcommands: Depends: postfix but it is not installable

Removing all exim4 packages fixes the problem, however I would like to
ask:

 * aptitudes says I have held broken packages. `dpkg --get-selections` 
   says I have no held packages at all. Is this a (small) bug in 
   aptitude?

 * Why is my package considered "broken"? All dependencies are correct. 
   Should it explicitly conflict with exim4? (I think this is pointless 
   since postfix already does.)

 * How can I make aptitude to remove exim4 when installing 
   morg-mailcommands?

Even the -f flag to aptitude doesn't help.

Thanks,
--
Szabolcs