[Dovecot] Setting up webmail in DMZ

I have a Smoothwall server on my network and am running three network interfaces off it.

1. local LAN 192.168.0.0 with PCs and an internal dovecot server on 192.168.0.154.
2. internet interface
3. DMZ 192.168.2.0 which has a linux web server 192.168.2.1 on which I want to install a webmail so I can access my email remotely.

Originally 192.168.2.1 couldn't see the 192.168.0.0 network but with some help from the Smoothwall forums I have fixed that. The problem now is that 192.168.2.1 can't connect to the dovecot server on 192.168.0.154. When I "telnet 192.168.0.154 993" or "telnet 192.168.0.154 143" I get a "Connection refused" error. But these commands work fine from PCs on the 192.168.0.0 network.

I'm pretty sure there's no firewall on the dovecot server and /etc/hosts.allow and /etc/hosts.deny are empty.

Is there a default setting that I need to change in Dovecot that only allows connections from machines on the same subnet?