Outlook Web Access (OWA) works in front-end/back-end Exchange Server deployments, but you need to pay extra attention to maintenance if you're running this setup. This is doubly important for updates and service packs, which should always be applied to front-end servers and back-end servers in synchrony. Otherwise, you could run into OWA performance and availability problems.
If you improperly or inconsistently update your front-end and back-end servers, OWA users may receive a "Loading" message when they try to access their mailboxes from the front-end server -- but no messages will ever actually display, and reloading will not help.
This problem typically arises when the back-end server is updated without the front-end server also being patched. It is also important to note that the proper order of operations is to always upgrade your front-end servers before your back-end servers. See Microsoft TechNet article, Service Packs: Upgrading front-end and back-end servers.
A quick way to bring your front-end and back-end servers into synchrony is to examine the contents of the \Program Files\Exchsrvr\exchweb folder on each of them. Usually, the directory will have a few folders with revision numbers in them, such as 6.5.6944.0 and 6.5.7226.0. The most recent updates are in the highest numbered folders.
You can then copy the folders from the back-end server and paste them into the exchweb folder on the front-end server. If you have more than one front-end server, make sure you do this for all of them. (You do not need to restart Exchange Server when you're done.)
The best long-term solution is, of course, to patch both machines, but the above workaround is useful if you want to get things working without going through the downtime required to patch Exchange Server.
About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.
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Related information from SearchExchange.com:
Tutorial: How to set up a front-end Exchange Server cluster
Expert Advice: Deciding between a front-end and back-end Exchange server
FAQ: Outlook Web Access administration
Learning Center: Troubleshooting Outlook Web Access
Reference Center: Outlook Web Access tips and resources
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