Messaging extensions are already available in Microsoft Teams. At Build 2021, Microsoft today announced the support for Messaging extensions in Outlook on the web. With this support, when users compose a new message in Outlook on the web, they will be able to select a new menu of search-based messaging extensions to choose from. Developers can reuse their Microsoft Teams messaging extension in Outlook on the web.
For example, a user may be able to compose an email and then select a message extension that surfaces tasks from their Teams app to send to teammates