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.

Guidelines for Outlook add-in and message extension

Outlook add-in

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.

Message extension

Create a message extension if your app requires any of the following scenarios:

• Ability to work in both Teams chat and Teams calendar items, as well as Outlook email messages and calendar items.
• Ability to use Adaptive Cards as the canvas for the inserted content.
• Ability to use link unfurling, that is, to insert a rich preview of a link.

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

See also

• Extend Teams apps across Microsoft 365
• Extend a Teams message extension across Microsoft 365