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Configure your Outlook add-in for event-based activation

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The event-based activation feature lets a user use your add-in to complete their tasks without explicitly launching the add-in. Your add-in will run tasks when certain events occur, such as automatically update a mail item's attachments when the recipients change or check for a particular attachment before a mail item is sent. You can also integrate event-based activation with the task pane and function commands.

Note

Support for this feature was introduced in requirement set 1.10, with additional events now available in subsequent requirement sets. For details about an event's minimum requirement set and the clients and platforms that support it, see Supported events and Requirement sets supported by Exchange servers and Outlook clients.

To learn how to implement an event-based add-in that runs in Outlook on mobile devices, see Implement event-based activation in Outlook mobile add-ins.

Supported events

The following table lists events that are currently available and the supported clients for each event. When an event is raised, the handler receives an event object which may include details specific to the type of event. The Description column includes a link to the related object where applicable.

Event canonical name
and XML manifest name		 Unified manifest for Microsoft 365 name Description Minimum requirement set and supported clients
OnNewMessageCompose newMessageComposeCreated On composing a new message (includes reply, reply all, and forward) but not on editing, for example, a draft. 1.10

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
- Android2
- iOS2
OnNewAppointmentOrganizer newAppointmentOrganizerCreated On creating a new appointment but not on editing an existing one. 1.10

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnMessageAttachmentsChanged messageAttachmentsChanged On adding or removing attachments while composing a message.

Event-specific data object: AttachmentsChangedEventArgs		 1.11

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnAppointmentAttachmentsChanged appointmentAttachmentsChanged On adding or removing attachments while composing an appointment.

Event-specific data object: AttachmentsChangedEventArgs		 1.11

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnMessageRecipientsChanged messageRecipientsChanged On adding or removing recipients while composing a message.

Event-specific data object: RecipientsChangedEventArgs		 1.11

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnAppointmentAttendeesChanged appointmentAttendeesChanged On adding or removing attendees while composing an appointment.

Event-specific data object: RecipientsChangedEventArgs		 1.11

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnAppointmentTimeChanged appointmentTimeChanged On changing date/time while composing an appointment.

Event-specific data object: AppointmentTimeChangedEventArgs

Important: If you drag and drop an appointment to a different date/time slot on the calendar, the OnAppointmentTimeChanged event doesn't occur. It only occurs when the date/time is directly changed from an appointment.		 1.11

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnAppointmentRecurrenceChanged appointmentRecurrenceChanged On adding, changing, or removing the recurrence details while composing an appointment. If the date/time is changed, the OnAppointmentTimeChanged event also occurs.

Event-specific data object: RecurrenceChangedEventArgs		 1.11

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnInfoBarDismissClicked infoBarDismissClicked On dismissing a notification while composing a message or appointment item. Only the add-in that added the notification will be notified.

Event-specific data object: InfobarClickedEventArgs		 1.11

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnMessageSend messageSending On sending a message item. To learn more, try the Smart Alerts walkthrough. 1.12

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnAppointmentSend appointmentSending On sending an appointment item. To learn more, see Handle OnMessageSend and OnAppointmentSend events in your Outlook add-in with Smart Alerts. 1.12

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnMessageCompose messageComposeOpened On composing a new message (includes reply, reply all, and forward) or editing a draft. 1.12

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnAppointmentOrganizer appointmentOrganizerOpened On creating a new appointment or editing an existing one. 1.12

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnMessageFromChanged messageFromChanged On changing the mail account in the From field of a message being composed. To learn more, see Automatically update your signature when switching between Exchange accounts. 1.13

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnAppointmentFromChanged appointmentFromChanged On changing the mail account in the organizer field of an appointment being composed. To learn more, see Automatically update your signature when switching between Exchange accounts. 1.13

- new Outlook on Windows (preview)
- Web browser
- New Mac UI
OnSensitivityLabelChanged sensitivityLabelChanged On changing the sensitivity label while composing a message or appointment. To learn how to manage the sensitivity label of a mail item, see Manage the sensitivity label of your message or appointment in compose mode.

Event-specific data object: SensitivityLabelChangedEventArgs		 1.13

- Windows (classic1 and new (preview))
- Web browser
- New Mac UI
OnMessageReadWithCustomAttachment Not available On opening a message that contains a specific attachment type in read mode. Preview3

- Windows1
OnMessageReadWithCustomHeader Not available On opening a message that contains a specific internet header name in read mode. Preview3

- Windows1

Note

1 Event-based add-ins in Outlook on Windows require a minimum of Windows 10 Version 1903 (Build 18362) or Windows Server 2019 Version 1903 to run.

2 Outlook on mobile supports APIs up to Mailbox requirement set 1.5. However, support is now enabled for additional APIs and features introduced in later requirement sets, such as the OnNewMessageCompose event. To learn more, see Implement event-based activation in Outlook mobile add-ins.

3 To preview the OnMessageReadWithCustomAttachment and OnMessageReadWithCustomHeader events, you must install Outlook on Windows Version 2312 (Build 17110.10000) or later. Then, join the Microsoft 365 Insider program and select the Beta Channel option to access Office beta builds.

Troubleshoot your add-in

As you develop your event-based add-in, you may need to troubleshoot issues, such as your add-in not loading or the event not occurring. For guidance on how to troubleshoot an event-based add-in, see Troubleshoot event-based and spam-reporting add-ins.

Deploy to users

Event-based add-ins are restricted to admin-managed deployments only, even if they're acquired from AppSource. If users acquire the add-in from AppSource or the in-app Office Store, they won't be able to activate the event-based function of the add-in. To learn more about listing your event-based add-in in AppSource, see AppSource listing options for your event-based Outlook add-in.

Admin deployments are done by uploading the manifest to the Microsoft 365 admin center. In the admin portal, expand the Settings section in the navigation pane then select Integrated apps. On the Integrated apps page, choose the Upload custom apps action.

The Integrated apps page on the Microsoft 365 admin center with the Upload custom apps action highlighted.

Important

Add-ins that use the Smart Alerts feature can only be published to AppSource if the manifest's send mode property is set to the prompt user or soft block option. If an add-in's send mode property is set to block, it can only be deployed by an organization's admin as it will fail AppSource validation.

Deploy manifest updates

Because event-based add-ins are deployed by admins, any change you make to the manifest requires admin consent through the Microsoft 365 admin center. Until the admin accepts your changes, users in their organization are blocked from using the add-in. To learn more about the admin consent process, see Admin consent for installing event-based add-ins.

Event-based activation behavior and limitations

Add-in launch-event handlers are expected to be short-running, lightweight, and as noninvasive as possible. After activation, your add-in will time out within approximately 300 seconds, the maximum length of time allowed for running event-based add-ins. To signal that your add-in has completed processing a launch event, your associated event handler must call the event.completed method. (Note that code included after the event.completed statement isn't guaranteed to run.) Each time an event that your add-in handles is triggered, the add-in is reactivated and runs the associated event handler, and the timeout window is reset. The add-in ends after it times out, or the user closes the compose window or sends the item.

If the user has multiple add-ins that subscribe to the same event, the Outlook platform launches the add-ins in no particular order. Currently, only five event-based add-ins can be actively running.

In all supported Outlook clients, the user must remain on the current mail item where the add-in was activated for it to complete running. Navigating away from the current item (for example, switching to another compose window or tab) terminates the add-in operation. However, an add-in that activates on the OnMessageSend event handles item switching differently depending on which Outlook client it's running on. To learn more, see the "User navigates away from current message" section of Handle OnMessageSend and OnAppointmentSend events in your Outlook add-in with Smart Alerts.

In addition to item switching, an event-based add-in also ceases operation when the user sends the message or appointment they're composing.

When developing an event-based add-in to run in the Outlook on Windows client, be mindful of the following:

  • Imports aren't supported in the JavaScript file where you implement the handling for event-based activation.

  • Add-ins don't run code included in Office.onReady() and Office.initialize. We recommend adding any startup logic, such as checking the user's Outlook version, to your event handlers instead.

  • Only the JavaScript file referenced in the manifest is supported for event-based activation. You must bundle your event-handling JavaScript code into this single file. The location of the referenced JavaScript file in the manifest varies depending on the type of manifest your add-in uses.

    • XML manifest: <Override> child element of the <Runtime> node
    • Unified manifest for Microsoft 365 (preview): "script" property of the "code" object

    Note that a large JavaScript bundle may cause issues with the performance of your add-in. We recommend preprocessing heavy operations, so that they're not included in your event-handling code.

Some Office.js APIs that change or alter the UI aren't allowed from event-based add-ins. The following are the blocked APIs.

Preview features in event handlers (Outlook on Windows)

Outlook on Windows includes a local copy of the production and beta versions of Office.js instead of loading from the content delivery network (CDN). By default, the local production copy of the API is referenced. To reference the local beta copy of the API, you must configure your computer's registry. This will enable you to test preview features in your event handlers in Outlook on Windows.

  1. In the registry, navigate to HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\Options\WebExt\Developer. If the key doesn't exist, create it.

  2. Create an entry named EnableBetaAPIsInJavaScript and set its value to 1.

    The EnableBetaAPIsInJavaScript registry value is set to 1."

Enable single sign-on (SSO)

To enable SSO in your event-based add-in, you must add its JavaScript file to a well-known URI. For guidance on how to configure this resource, see Use single sign-on (SSO) or cross-origin resource sharing (CORS) in your event-based or spam-reporting Outlook add-in.

Request external data

You can request external data by using an API like Fetch or by using XMLHttpRequest (XHR), a standard web API that issues HTTP requests to interact with servers.

Be aware that you must use additional security measures when using XMLHttpRequest objects, requiring Same Origin Policy and CORS (Cross-Origin Resource Sharing).

Note

Full CORS support is available in Outlook on the web, Mac, and Windows (starting in Version 2201, Build 16.0.14813.10000).

To make CORS requests from your event-based add-in, you must add the add-in and its JavaScript file to a well-known URI. For guidance on how to configure this resource, see Use single sign-on (SSO) or cross-origin resource sharing (CORS) in your event-based or spam-reporting Outlook add-in.

See also