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Last Updated: June 16, 2020


When clicking on items in the Conversation History folder, Outlook hangs or shows the "Not responding" error message. The issue may also occur when clicking other emails with custom message classes, such as Skype items and voice mail emails.


When Outlook encounters a certain combination of errors trying to resolve a message class, Outlook will go check the Organizational Forms library on the Public Folder server to ensure the correct message class is available. This introduces an extra call out to the Public Folder server to resolve the message class.  Due to delays in Autodiscover and public folder response times this can cause Outlook to hang. An example message class from recent reports is IPM.Note.Microsoft.Conversation. This problem can also be exaggerated if the Public Folders are unavailable, not optimally configured or if they are on older unsupported versions of Exchange 2007.

Support has identified three possible client side workarounds. Each of these eliminates a default Outlook function and largely or fully eliminates the hang:


HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover DWORD: ExcludeHttpsAutoDiscoverDomain VALUE: 1

Reference KB 2212902


This option disables the Organizational Forms Library functionality in Outlook completely. This is a good option to use if Outlook does not need to access the Organizational Forms Library at all.

DWORD: DisableOrganizationalForms


This option allows you to specify that Outlook should not look for specific custom forms for certain message classes. This is a good option to use when you have other items in the Organizational Forms Library that you still need to allow Outlook to access.

PATH: The path depends on the combination of the bitness (32-bit/64-bit) of Outlook and Windows. When the bitness differs, it needs to be under the WOW6432Node key. When the bitness is the same (both 64-bit or both 32-bit), then it doesn’t need to be under that key.

Outlook and Windows are on a different bitness


Outlook and Windows are on the same bitness


DWORD: <the name of the message class, including a separate DWORD for each custom word in the message class> VALUE: 1

For example with the “IPM.Note.Microsoft.Conversation” message class, you would need to add the following DWORDS, both with Value 1:

  • IPM.Note.Microsoft

  • IPM.Note.Microsoft.Conversation

For example with the “IPM.Note.Custom.Voice.Mail.Email” message class, you would need to add the following DWORDS, all with Value 1:

  • IPM.Note.Custom

  • IPM.Note.Custom.Voice

  • IPM.Note.Custom.Voice.Mail

  • IPM.Note.Custom.Voice.Mail.Email

Note: You can determine the message class of an item in Outlook with these steps:

  1. Right click the column headers in the email list and click Field Chooser.

  2. Select All Mail fields and find Message Class in the list.

  3. Select and drag Message Class to the column headers, then drop it to add it as a column.

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See Also

Fixes or workarounds for recent issues in Outlook for Windows

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