You can use an IMAP4 client or a POP3 client in following format to log on to a delegate mailbox that is hosted on a version of Exchange Server that is earlier than Microsoft Exchange Server 2007:
However, this functionality is not supported in Exchange Server 2007. When you use an IMAP4 client or a POP3 client to log on to a delegate mailbox of Exchange Server 2007 in the previous format, you receive an error that resembles the following:
The server has rejected your login. Please verify that your user name and password are correct. Error Code: 800cccd1
To resolve this problem, download Update Rollup 4 for Exchange Server 2007 Service Pack 1. For more information about Update Rollup 4 for Exchange Server 2007 Service Pack 1, see the following Exchange Help topic:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
You may also receive an error when a user tries to access a delegate or shared mailbox, and the POP3 protocol is disabled. Consider the following scenario:
User 1 is a mailbox user who has Full Mailbox Rights on a shared mailbox that is named Shared1.
The POP3 protocol is disabled on User 1's mailbox.
TheShared1 mailbox is hosted on Exchange Server 2007 or Exchange Server 2010.
A user tries to access the Shared1 mailbox by using User 1's credentials in the form of domain\User1\Shared1.
In this scenario, the user receives an error message that resembles the following:
-ERR Logon failure: unknown user name or bad password.
Additionally, entries that resemble the following are logged in the Extrace log:
Pop3 Session UserConfiguration Microsoft.Exchange.Pop3.Pop3ProtocolUser > Pop3 Session User domain/user1 is not enabled for protocol access. > Pop3 Session Failed to login user domain/user1. > Pop3 Session <<< Response sent: -ERR Logon failure: unknown user name or bad password.
This issue occurs because Exchange Server validates the POP3 protocol if the POP3 protocol is enabled or disabled.
Note This issue does not occur in Microsoft Exchange Server 2003 and earlier Exchange Server versions.