If you will only connect using Outlook Anywhere the only ports you will need to forward is https on 443. You will probably also want to forward http on port 80 to allow the auto-forward of web browser requests to the secure channel as a convenience to your users.
Other ports for imap, pop and smtp are not needed in an Outlook Anywhere deploy.
On the SSG you will need to have a public address you can forward the ports from with your ISP. This can also be your SSG public interface if you change the port used by management.
There are many methods for this inbound destination nat for a server. Check out kb11910 which walks you through some questions. Based on your answers this will give you the specific configuration kb article for your situation.
http://kb.juniper.net/InfoCenter/index?page=content&id=KB11910