Can't save a meeting as a draft in Outlook for Mac by using Office JS API

Original KB number:   4505745

Microsoft Outlook for Mac doesn't support saveAsync on a meeting in Compose mode. Outlook add-ins can't get the item identifier. It means that the add-ins can't uniquely identify and communicate with Microsoft Exchange to update or listen for changes on the item.

To work around this issue, you can set an extended property (customProperty: Office JS API) on the item. An extended property is part of the item and is available on Exchange as soon as the item is sent. Therefore, the add-in can query or listen to items that have this extended property set.

To set the property, follow these steps:

1. Select one of the following APIs to use:

   1. EWS
   2. REST
   3. Graph

2. Get a valid token for each API set:

   1. EWS: Use getCallbackTokenAsync
   2. REST: Use getCallbackTokenAsync with options.isRest = true
   3. Graph: Use onBehalfOf token

3. Query or listen for calendar events:

   1. EWS: Subscribe to the created event
   2. REST: Subscribe to the created notification, and filter based on the extended property
   3. Graph: Subscribe to the created notification, and filter based on the extended property

4. Find the corresponding extended property on Exchange:

   1. EWS:

      ExtendedFieldURI {PropertySet = PS_PUBLIC_STRINGS, PropertyName = cecp-<add-in id from manifest>}

   2. REST/Graph:

      SingleValueExtendedProperties { PropertyId = String {00020329-0000-0000-c000-000000000046} Name cecp-<add-in id from manifest>}

5. Use the notification that's sent to the webhook to update the backend with itemId when the subscription is successful.