How to remove exim4 when aptitude doesnt think its installed?

[Andy <andy@besy.co.uk>]

Hello List,

How should I go about removing files relating to the exim4 package, when 
aptitude doesn't think the package is installed?

Let me explain...

I have restored a crashed system by first doing a Debian base install 
and then restoring the file system from backup over the top. The result 
has been a fully functional system. (yay!)

But I have a few files left over from the Debian base install which 
should no longer be present, for instance files relating to the exim4 
package.

I had previously replaced exim4 with postfix, but because the file 
system restore process only creates and over-writes files, but doesn't 
deletes unnecessary ones, the exim4 files remain.

I cannot use aptitude to remove the package's files as normal because 
aptitude's state has been restored from backup along with everything 
else; it doesn't think the package is installed.

Any suggestions?

Many Thanks, Andy