Getting Teams Chat History Messages (Compliance Records) From a Mailbox using EWS and/or in Outlook Add-in
Microsoft made a recent change to where the compliance messages get stored in a Mailbox for private Teams Chats from the \Conversation History\Teams Chat Folder to a non_ipm_subtree folder called TeamsMessagesData (see https://office365itpros.com/2020/10/14/microsoft-changes-location-teams-compliance-records/ for some good commentary on this change). In terms of programmatic access to these messages this change affects the ability of the Graph (and Outlook REST) Endpoints to access them. While you could never access the Folder directly with the Graph API (because of the FolderClass) the messages themselves would appear in the \Messages endpoint (this is because they where captured by the underlying AllItems Search folder that backs this endpoint). Now the messages are in the Non_IPM_Subtree you loose the ability of that Search Folder to access those messages. This first up broke my OWA add-in from https://gsexdev.blogspot.com/2019/03/microsoft-teams-private-chat-history.html that