[exim] Upgrading from 3.36 to newest exim 4

Hey

Is there any things i should be very aware of when upgrading. Im using
quite a large number of virtual domains and running mail services for some
3000 people. Are there any holes i should be prepared to handle ?

I have read about the problems when converting and exim3 conf to exim4 but
i cannot find any page that describes the main differences. Is there any ?

--
Med venlig hilsen / Best regards
Lasse Birnbaum Jensen