Exchange 2010 Exchange Server name appears as Instance – <GUID>

Current Status: Issue – no issue

A few customers, partners, and individual folks in the community have reported that a few of the Exchange 2010 users 2003 randomly have connecting to their mailbox. After examining the mail profile in Outlook 2003, you can see the server name appears as Instance-<GUID> where <GUID> is a randomly generated GUID (or number). Re-resolving (‘Check Name’) the appropriate server name in the Outlook mail profile resolves the issue.

Figure 11: Instance-GUID issue in 2003

Seeing Instance-<GUID> in conversation between an 2003 client and an 2010 server is normal (when Instance-<GUID> appears inside Outlook in the folders list on left hand side); It does NOT mean you are hitting this particular issue. You experience this issue if the mail profile gets to refer to the server as Instance-GUID.

The problem behavior can be triggered by networking issues, patch applications, server reboots, etc. It requires 2003 to lose connectivity to and have a delegate mailbox logon attempted on a connection before the primary mailbox logon is attempted on that connection. This can affect users who are accessing shared mailboxes or folders of other users from their Outlook 2003 while connecting to Exchange 2010.

Currently there is no proper resolution available for this issue. However, to remediate this issue temporarily, simply re-resolve the server name in the mail profile. If possible, you may also remove the shared mailboxes or shared folders (like calendars) from the profile, preventing this issue from occurring in the future or create a new mail profile in Outlook.

is working to investigate this issue for a fix. You can contact Microsoft Support to report this issue and request further assistance. Currently no KB article exists for this issue.


has confirmed this to be a and the bug was assigned to the team within Microsoft. It has been fixed and a hotfix can be downloaded here:


Special Thanks to Henrik Walther & Jaap Wesselius

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