[Dovecot] Convert plugin

[Egbert]

Hi,
I'm trying to convert users from a sendmail server to a postfix/dovecot 
server. All works fine but one of the last things is to rescue the 
messages in /var/mail/<user> on the old server. This seems very 
straitforward using the convert plugin but with the settings from the 
wiki, nothing happens when the user logs in. Do I need a private 
namespace for this as suggested elsewhere in the wiki?

I experimented with mb2md.pl and that seems to do what we need but 
having the old mail converted upon login is much more attractive. In 
that way we hope that we can also find some 'dead' users.

TIA
Egbert Jan