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Scenarios for creating an Outlook add-in and a message extension

An Outlook add-in and a message extension allow you to create rich and interactive content for email messages and meeting invitations. You can create an Outlook add-in and a message extension for your Teams app based on the scenario.

If your app includes scenarios from Outlook add-in and message extension, then you must create both apps, an Outlook add-in and a message extension. You must host both these apps at the same domain so that they can share files.

Note

Agents provide a more flexible, intelligent, and future‑ready experience that enables richer reasoning, simpler development, and better alignment with the evolving Teams and Microsoft 365 platform. We recommend that you explore and build agents.

For more information, see build declarative agents and build agents in Teams.

If you have an existing bot-based message extension, you can extend it as an agent as well.

Guidelines for Outlook add-in and message extension

Create an Outlook add-in if your app requires any of the following scenarios:

  • Access to the properties of email messages or calendar items.
  • Ability to respond automatically to changes in the properties of email messages or calendar items.
  • Access to the content of email messages and calendar items with fine-grained read or write access that is provided by Outlook add-in APIs.
  • Read or write access to the user's mailbox using the Outlook add-in APIs.
  • Ability to start up automatically in response to events without explicit user action. For more information, see Event-based activation.
  • Ability to manipulate Outlook-specific settings, such as custom properties and internet headers.
  • Ability to run within messages and calendar items in shared mailboxes or shared folders.

Scenarios for Outlook add-in and message extension

The following examples show the recommended app type for different scenarios based on the task:

Customer relation management

Scenario App type
Save a lead that came on email into Customer Relation Management (CRM). Outlook add-in
Find and insert lead details into an email or meeting invitation. Message extension
Insert boilerplate responses from CRM into message or invitation body. Message extension
Track email open rates (by inserting a tracking pixel). Outlook add-in
Log email or meeting or engagement in Outlook into CRM. Outlook add-in

Security

Scenario App type
Mark an email as spam. Outlook add-in
Send test or mock emails for training and tracking action rates. Outlook add-in
Read or set the Microsoft Information Protection (MIP) label on an email based on business rules. Outlook add-in
Encrypt and decrypt emails and attachments based on business rules. Outlook add-in

Attachment management

Scenario App type
Save attachments in email into cloud storage.  Outlook add-in
Attach files from cloud storage to a message or invitation. Message extension

Meeting management

Scenario App type
Insert a meeting link into an invitation. Outlook add-in
Customize a meeting link based on the recipients, the meeting time, and other contextual facts. Outlook add-in
Update a meeting link when the meeting is updated. Outlook add-in
Reply with a Meet Now invitation. Message extension

Signature management

Scenario App type
Insert a signature in mail message automatically. Outlook add-in
Customize a signature based on the recipients, new thread or reply, and other contextual facts.  Outlook add-in
Synchronize a signature across devices. Outlook add-in
Enable administrator management of signatures for an organization. Outlook add-in
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