First an observation - close port 110; it's no longer needed as it's an old protocol. Also, if you've got the SSL versions of the IMAP ports open (and configured), I wouldn't leave the non-secure versions open .. it defeats the object .. and the same goes for the POP ports.

Now to your problem .. and a question .. you don't say how you your COS machine is physically connected to the internet .. is it via a separate router? - and if so, have you remembered to port forward port 25 to your server? If you haven't, then it matters not that your firewall has the port open, no traffic will reach it.