email options and --force with dpkg

[john gennard <joney@clara.co.uk>]

Following helpful replies from Kent(ktb) and Steve Gran to a 
request under the subject of 'email options', I've been looking 
further into the possibilities.  

I want to try qmail which I've found and built. It will not install
as it conflicts with ssmtp - seems I can have only one MTA.
Dselect will not uninstall ssmtp as the MUA's 'will feel lonely'.
So presumably I will have to either temporarily remove the MUA's
and replace ssmtp with qmail ( I haven't tried that, but, even if it
works, I don't like the idea as I want to try other MTA's until I
find one I understand and like) or force dpkg to uninstall ssmtp.

Both the man page and dpkg --help are unclear to me, and I don't
want to risk damage. Could someone help with the precise syntax to
force remove and purge ( ssmtp in this case ).  

Or am I labouring under a misunderstanding ( kmail, which I've used
for a long time, doesn't appear to enter into the conflict).

Grateful for any advice,        John.