Thats ok, postfix is listening on all interfaces.
So the connecion must be blocked by a firewall, this can be the firewall on the server itself. Test it with:
A firewall in a router in front of the server or a firewall of your internet acccess provider. Many providers block port 25 to avoid spam, so if your server is not located in a datacenter, then its likely that your provider blocks the smtp connections.