You are unexpectedly prompted for your user credentials in Outlook 2003

You are unexpectedly prompted for your user credentials in Microsoft Office Outlook 2003. Additionally, if you click Cancel in the Enter password dialog box, Outlook 2003 switches to offline mode.

This behavior occurs if the computer loses network connectivity for some time and then reestablishes network connectivity. When this behavior occurs, Outlook 2003 tries to establish a TCP/IP connection to the server that is running Microsoft Exchange Server as soon as the network is available again. If the network adaptor is not ready, the attempt by Outlook 2003 fails. When the first attempt fails, Outlook 2003 tries to establish an RPC/HTTP connection. If RPC/HTTP is configured to use basic authentication, you are prompted for your user credentials.

To prevent Outlook 2003 from switching to offline mode, type the user name and the password in the Enter password dialog box. Then, click OK.

To reduce the chances that you will be prompted for your user credentials, select NTLM Authentication for the RPC/HTTP proxy authentication settings. However, this action does not guarantee that this behavior will not occur again.

Sometimes, the connection may fail after you provide your credentials. This failure can occur if the network stack is not yet ready. You will be able to connect by using Outlook 2003 after network connectivity is reestablished.

Typically, this behavior occurs when the computer is put in hibernation and then resumes from hibernation because of user activity. Up to two minutes may be required to establish network connectivity after the computer resumes from hibernation.

Steps to reproduce the behavior

Configure Outlook 2003 in cached mode to connect by using RPC/HTTP with basic authentication.

Make sure that you configure Outlook 2003 to try HTTP only after Outlook 2003 uses TCP/IP. To do this, follow these steps:

1. Start Outlook 2003.
2. On the Tools menu, click E-mail Accounts.
3. Click View or change existing e-mail accounts, and then click Next.
4. Click the Exchange Server e-mail account, and then click Change.
5. Click More Settings, and then click the Connection tab.
6. In the Exchange over the Internet area, click to select the Connect to my Exchange mailbox using HTTP check box, and then click Exchange Proxy Settings.
7. Verify that the On slow networks, connect using HTTP first, then connect using TCP/IP, check box is not selected.
8. In the Proxy authentication settings area, click Basic Authentication in the Use this authentication when connecting to my proxy server for Exchange box.
9. Click OK two times.
10. Quit Outlook 2003.
11. Make sure that you are connected to the network. Then, start Outlook 2003.
12. Wait for Outlook 2003 to connect to the Exchange server. Verify that the connection is a TCP/IP connection. To do this, follow these steps:
    1. Press and hold CTRL, right-click the Outlook icon in the notification area, and then click Connection Status.
    2. Verify that the Conn column displays TCP/IP.
13. Put the computer on standby.
14. Resume the computer from standby. Then, wait for about one minute.
15. You are prompted for your user credentials.
16. Click Cancel.

Outlook switches to offline mode.