How to Enable AutoDiscover for Outlook 2007
After reading the article: http://technet.microsoft.com/en-us/library/bb124251(EXCHG.80).aspx, particularly the part that states "Depending on whether you have configured the Autodiscover service on a separate site, the Autodiscover service URL will be either https://<smtp-address-domain>/autodiscover/autodiscover.xml or https://autodiscover.<smtp-address-domain>/autodiscover/autodiscover.xml." I decided to create a DNS record for autodiscover and open the firewall so that it could obtain that information. Noteworthy is that you can setup the external URLs for OWA and Active Sync and I believe you use them here.
More Resources:
http://technet.microsoft.com/en-us/library/bb124251(EXCHG.80).aspx
http://technet.microsoft.com/en-us/library/bb430749(EXCHG.80).aspx
