The "Briefing" email from Microsoft Viva is a system generated email that is directly inserted into your mailbox by Microsoft. The information contained in the message is derived from your Outlook account and is private to you. It is enabled by default, however you can opt-out or unsubscribe.
See Also: Briefing Email Overview (microsoft.com)
To Disable the Daily Briefing Email
1. Locate the most recent email and click the "UNSUBSCRIBE" hyperlink in the footer of the message.
2. Adjust the Daily Briefing setting to OFF