Currently, Sharing emails from the Inbox is not supported for Outlook-based users. To learn more about the Mixmax integration with Outlook, check out How to use Outlook with Mixmax.
When you click the Share button, as shown in the screenshot below, it creates a unique share URL (e.g., https://mail.mixmax.com/m/5m3VxNmUJ75NZdxRa). The ID on the URL is random, so it's nearly impossible to guess. The shared email is available on a web page, and you can choose who is able to view the link and expiration date:
To stop the email from being shared, click the trash can icon (see screenshot below) - that deactivates the link, and no one can access it.
