Assume that domain users connect to Microsoft Exchange Server by using Microsoft Outlook. The Outlook Anywhere feature is enabled in their Outlook profiles. When the domain users switch from using the LAN to using a wide area network (WAN), they are prompted for credentials by Outlook.
This issue occurs when the client authentication method of Outlook Anywhere is set to Basic Authentication on the Exchange server.
When the user switches to another network, Outlook may change the connection type from TCP to HTTPS. If the client authentication method of Outlook Anywhere is set to Basic Authentication, the user is prompted for credentials.
To resolve this issue, set the client authentication method of Outlook Anywhere to NTLM Authentication on the Exchange server.
For more information about how to configure Outlook Anywhere on an Exchange server, go to the following Microsoft websites:
Microsoft Office Outlook 2007, Microsoft Outlook 2010, Microsoft Outlook 2013, Microsoft Exchange Server 2010 Enterprise, Microsoft Exchange Server 2010 Standard, Microsoft Exchange Server 2007 Enterprise Edition, Microsoft Exchange Server 2007 Standard Edition