Outlook web access only works in intranet / Exchange Server

I set up the SBS 2003 server, with exchange. I got access problem

1) I use outlook web access, but only can use in intranet computer.  The
PC 
outside the newtwork is not allowed to access the page. Why.
- The firewall should be opended for all ****ts already
- Any relation to the the IIS setting, Directroy security, should i use 
[allow annoymous access] or use [ Auth by domain ] ?

2) I cannot connect to the Exchange server by IMAP, would this sup****t ?

Thanks