Juniper SRX begining setup

Greetings Experts,

I'm transitioning from Juniper SSG to SRX and it's a little different.  I have a new SRX 210 where I was able to do the basic configuration via the GUI and get the Internet working.

I need to get mail to pass to my exchange server.  I only have one Static IP which the Juniper is using.

What I did was add an address to the address book to the Internal zone.  Problem is when I put in the IP it comes up with the wrong subnet.  I inherited this network 10.0.0.0 / 24.  Juniper = 10.0.0.100 and server = 100.0.0.5.  When I add the address to the address book, it comes up / 32.  I try to change it to /24, but get an error when committing.

So I added the rules via the wizard and can see them when I go to policy.  internet - new internal address.  Permit junos-mail.
Internet is working, mail is not routing.  Any idea?  Can this be done via the gui or do I need to learn the cli?  I usually use Telnet for the ssg, but this is slightly different.

Any help would be most appreciated,
Kacey