When exploring Teams channel messages, some messages are listed with an empty Author and Subject value. Attempting to preview one of these messages causes the following warning to be displayed:

System event messages are unsupported.

Microsoft Teams generates system messages to provide insights into various team events, including member additions to chats, changes in team names, updates to channel descriptions, and meeting or call-related activities. These system messages are exposed by the Microsoft Graph API and are included alongside user messages for a Teams channel without any method to filter by message type. Consequently, when Veeam Backup for Microsoft 365 leverages the Microsoft Graph API to back up Teams channel messages, it also captures the system messages.

Note: During export and restore operations, such messages are silently skipped.