There is a newer issue of thie ISPmail guide available if you are using Debian Jessie!
Split up the Dovecot configuration
The configuration syntax used in Dovecot 2.x is very different from what you are used. Instead of a single dovecot.conf file different parts are now configured in several different files. Please read the section about the Dovecot configuration to see how you need split up the dovecot.conf file that you were using previously.
Remove Avelsieve and Squirrelmail
The ISPmail guide for Lenny contained instructions on setting up a webmail service using Squirrelmail. It also used the Avelsieve plugin for Squirrelmail to allow your users to configure their server-side email rules. I have to admit that I did not cover webmail access in the Squeeze tutorial at all – shame on me. However in this Wheezy tutorial I am using the beautiful Roundcube webmail application that has simple and direct access to the server-side email rules managed by Dovecot directly. So please remove the old packages:
apt-get –purge remove avelsieve squirrelmail