IMPORTANT: This article was published before the release of:
Exchange 2010 SP3 Update Rollup 3
Exchange 2007 SP3 Update Rollup 12
These update rollups fix the problem discussed here for Exchange 2007 and 2010.

This problem concerns all Exchange versions from 2003 to 2013. This weekend I tested various Exchange servers to see exactly what the problem status is. My test results tell me that a fix is available for Exchange 2013 and a workaround is available for Exchange 2007 and 2010. Exchange 2003 was not tested.

Internet Explorer 11 is the new IE version shipping with Windows 8.1. So far Windows 8.1 RTM availability was limited to Microsoft partners and the developer community. However we are now only a few days away from public availability. In addition, IE11 is also going to be pushed onto desktops as an important Windows Update. Here is what Microsoft says in this regard:

To help our customers become more secure and up-to-date, Microsoft will distribute Windows Internet Explorer 11 as an important update through Automatic Updates for Windows 7 SP1 and higher for x64 and x86 and Windows Server 2008 R2 SP1 and higher for x64.

All Exchange administrators should thus follow the deployment of IE11 closely. Although OWA Light is a decent interface, users working with OWA Premium won't be happy with the switch. Apart for being more feature rich, OWA Premium also provides access to 3rd party OWA extensions. So if your organization depends on add-ons such as OWA Recall, users won't find this functionality integrated into OWA Light.

Test Results

Here are all the Exchange versions I tested together with the OWA interface.

I only got OWA Premium in case of Exchange 2013 CU2. Exchange 2013 CU1 and earlier Exchange versions all returned OWA Light.

This is what the Exchange 2010 login page looks like. It is immediately clear that OWA Light is being served. Exchange 2007 also returns a similar login page showing the OWA Light checkbox. In Exchange 2013 we have to logon to the mailbox first in order to see which OWA interface is being served.

Blocking Internet Explorer 11

One possible solution is that of blocking the installation of Internet Explorer 11 until a fix is made available. Microsoft is providing a toolkit for blocking Automatic Updates from installing IE11:
Toolkit to Disable Automatic Delivery of Internet Explorer 11

Of course organizations that manage updates through Windows Server Update Services (WSUS) or System Center can block this update without using this tool.

Workaround

For those who cannot live without Windows 8.1 or those who still want to upgrade to IE11 a workaround is also available. We basically have to configure Internet Explorer to load OWA in Compatibility View mode. At Internet Explorer configure this under Tools | Compatibility View Settings.

Selecting the 'Display intranet sites in Compatibility View' checkbox solves the problem for internal OWA access. As for external access, we have to add the domain used to publish OWA to the outside world. Enter this at the 'Add this website' field and click Add.

Final Tips

Overall I am quite positive about Windows 8.1. Windows 8 users will certainly be looking forward to this upgrade. Windows 8.1 is also filling some blanks that could encourage the upgrade of more Windows XP and Windows 7 desktops.

So it would really be a pity if Internet Explorer 11 forces some organizations to delay the deployment of this upgrade.

On the other hand, anyone used to OWA Premium will not enjoy switching to OWA Light. If running Exchange 2013, consider deploying CU2 if not already done. As for Exchange 2010 and 2007 you may want to wait a bit. In my opinion Windows 8.1 is too important for Microsoft to allow such a problem to block its adoption. So it might not take long until a fix is available.