You receive error 0x800ccc90 or error 0x800ccc18 when you try to log on to Exchange Server by using Secure Password Authentication

When you try to log on to Microsoft Exchange Server with Outlook Express by using Secure Password Authentication, you may see the following error messages in Microsoft Outlook Express. Look in the Details of the Error tab after failing to connect. On the Exchange Server computer you will see the following Event IDs:

Either the Outlook Express POP3 client is not able to access the mailbox because it does not exist or there is a custom recipient in the Exchange Server organization that has the same alias as you do, and Exchange Server is attempting to access the custom recipient before accessing your mailbox.

In Outlook Express, try using Clear Text, which is the Log on using option under the Servers tab of the mail account.

To do so:

1. On the Tools menu, click Accounts. This will bring up several tabs.
2. If you select any listed mail account, the properties will have a Servers tab with the Log on using option.
3. Select the Clear Text option.

If this works, then you were trying to access a non-existent mailbox or the wrong mailbox. If this does not work, then the administrator needs to check for and remove the custom recipient.

When a user tries to log on to Exchange Server with Outlook Express and Secure Password Authentication, the client will pass the credentials of the user logged on to the workstation. If the logon works using the Clear Text option: <NT Domain/NT Account/Alias>, the user will have to change his or her mailbox alias to the Windows NT account name in order to use Secure Password Authentication. This is because Secure Password Authentication will not pass the mailbox alias information. It defaults to <NT DOMAIN\NTACCOUNT> and Exchange Server assumes the alias to be the Windows NT account.