You can't expand a nested contact group and Unknown is displayed in the group name in Outlook

  • Article
  • Applies to:
    Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, Outlook for Microsoft 365

Original KB number:   4293589

Symptoms

In Microsoft Outlook, you try to expand a contact group in a public folder that contains a nested contact group. However, the contact group doesn't expand, and the text <Unknown> appears at the end of the group name.

Screenshot of email address bar in Outlook when you expand two contact groups and the text Unknown appears at the end of the group name.

Resolution

Method 1

To resolve this issue, right-click the Contact folder in the Public Folder, and then select Properties. On the Outlook Address Book tab, select the Show this folder as an email address book option.

Method 2

  1. Open the contact group, and select Update now. If there are members that can't be found, Outlook will prompt you to select one of the following options:
  • Remove the lost members.
  • Try to repair the lost members and remove only those that cannot be resolved.
  • Cancel this operation and do not change any members.
  1. Select Try to repair the lost members and remove only those that cannot be resolved, and then select OK.

More information

A similar issue occurs if another user adds a contact group from their own contacts to the public folder contact group, and then a different user tries to send an email message to that contact group. This scenario is not resolved by the Show this folder as an email address book option.