Ask the Expert

Configuring OWA and OMA on ISA Server in a DMZ

I have Exchange 2003 and I want to enable Outlook Web Access (OWA) and Outlook Mobile Access (OMA) from ISA Server 2004. I don't want to keep ISA Server as a firewall. We already have a third-party firewall, and I'm planning to install ISA Server 2004 in a demilitarized zone (DMZ).

Do I need two network interface cards (NICs) in ISA Server or just one? How can I have ISA Server 2004 in a DMZ? I have found a lot of technical documents about ISA Server with Exchange Server, but they all have ISA Server as the firewall.

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Yes, you need to have two NIC cards to support the Reverse Proxy function of ISA Server for OWA and OMA. You can still have ISA Server in the DMZ of a third-party firewall. Regardless of the firewall you utilize to create the DMZ, ISA Server in the DMZ has become the recommended configuration from Microsoft for providing the best security for Exchange 2003. See the Microsoft article, Using ISA Server 2004 with Exchange Server 2003, for more information.


Actually you do not need two NICs for the Reverse Proxy function. This is one of the only configurations for ISA Server that does not require another NIC. We have this same setup in our environment where ISA Server is only used for Outlook Web Access (OWA), and we only have one NIC card installed.
—Daniel B.

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Related information from

  • Expert Advice: Setting up ISA servers
  • Expert Advice: Firewall recommendations and VPN support
  • Article: Should you use ISA Server as your Exchange firewall?
  • Step-by-Step Guide: How to use ISA Server as an SMTP filter
  • Reference Center: Exchange Server firewalls tips and resources
  • Reference Center: ISA Server tips and resources
  • This was first published in July 2006

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