My users are getting additional OWA login prompts, how can I fix this?

Additional login prompts are usually the result of a mismatch of IIS Authentication settings. The authentication settings for the Exchange, Public, and Exchweb\bin virtual directories must match to ensure users do not get additional login prompts.

It is best to check the Exchange and Public Authentication settings from the Exchange System Manager (ESM) and then compare them to the settings in the IIS Manager. This order is important since the ESM settings overwrite the IIS settings for the Exchange and Public virtual directories.

Compare the IIS authentication settings for the Exchange, Public, and Exchweb\bin virtual directories in Exchange System Manager (ESM) and the Internet Information Services Manager (IIS).

1. Open Exchange System Manager (ESM)
2. Navigate to the Exchange Virtual Server (\Administrative Groups\First Administrative Group\<Servers>\Protocols\HTTP\Exchange Virtual Server)
3. Right-click on the Exchange virtual directory, and select Properties
4. Change to the Access tab and click the Authentication button
5. Repeat steps 3 to 4 for the Public virtual directory
6. Open the IIS Manager
7. Navigate to the OWA website
8. Right-Click on the Exchweb\bin virtual directory, and select Properties
9. Change to the Directory Security tab
10. Click Edit under the Anonymous access and authentication control section
11. Verify that the Windows Authentication and Default Domain settings match those of the Exchange and Public virtual directories

Refer to the summary tables of IIS authentication settings below.

Native OWA virtual directory authentication settings