You've definitely got something blocking ports 25 & 7025, I can't telnet to them from here. There's a problem with your setup, does the router have a firewall and could it be blocking your connection?
I'm also slightly confused by your set-up, the DNS resolves to a different IP for mail.greenwayschool.co.uk than the error message from zimbra that you posted earlier which was for greenwayschool.co.uk. The IP at mail.greenwayschool.co.uk times out if I telnet to it and that leads me to believe there's something blocking your conection. If I telnet to port 25 at greenwayschool.co.uk there's a response from a mail server but then it gets closed. What's happening with your DNS or do you have two servers set-up?