RWWGuard is not designed to protect OWA directly, however this workaround will redirect the OWA logins to RWW.
Open “C:\Program Files\Exchsrvr\exchweb\bin\auth\owalogon.asp” with Notepad.
After the line that says “<% Language=VBScript %>”, add the following:
<% ' Added to force user to log onto RWW-Guard before accessing email remotely Response.Redirect( "/Remote/" ) %>
This will force a redirect to the RWW-Guard logon before allowing people to access OWA.
Note: These steps are for RWW running on SBS 2003. For RWW on SBS 2008, please see the SBS 2008 version of this article.