openTypeExtension resource type (open extensions)

Namespace: microsoft.graph


APIs under the /beta version in Microsoft Graph are subject to change. Use of these APIs in production applications is not supported. To determine whether an API is available in v1.0, use the Version selector.

Open extensions (formerly known as Office 365 data extensions) provide an easy way to directly add untyped properties to a resource in Microsoft Graph. Open extensions are represented by the openTypeExtension resource. Any open extension added to a resource shows up in the extensions navigation property, which is derived from the extension abstract type. Each extension has an extensionName property which is the only pre-defined, writable property for all extensions, along with your custom data. One way to help make sure extension names are unique is to use a reverse domain name system (DNS) format that is dependent on your own domain, for example, Com.Contoso.ContactInfo. Do not use the Microsoft domain (Com.Microsoft or Com.OnMicrosoft) in an extension name.

Open extension example: Add custom data to users using open extensions

Open extensions are supported by the following resources in the corresponding versions - general availability (GA: /v1.0 and /beta) or preview (/beta).

Resource Version
Administrative unit GA
Calendar event GA
Group calendar event GA
Group conversation thread post GA
Device GA
Group GA
Message GA
Organization GA
Personal contact GA
User GA
Task GA
Task list GA

Outlook-specific considerations

Each open extension present on an Outlook resource (event, message, or personal contact) is stored in a MAPI named property. When you create open extensions for Outlook, consider that MAPI named properties are a finite resource in a user's mailbox. When a user's named property quota is exhausted, you can't create any more named properties for that user. This can result in unexpected behavior from clients that rely on named properties to function.

Apply the following guidelines when you create open extensions on Outlook resources:

  • Create the minimum number of extensions required. Most applications should require no more than one extension. Extensions have no set defined properties or structure, so you can store multiple values in a single extension.
  • Avoid naming extensions in a variable manner (such as based on user input, etc.). Each time an open extension is created with a new name that has not been used in a user's mailbox before, a new MAPI named property is created. Removing the extension does not remove the named property.

Use open extensions (for Outlook resources) or extended properties

Open extensions are the recommended solution for most scenarios involving storing and accessing custom data. If, however, you need to access custom data for Outlook MAPI properties that are not already exposed through the Microsoft Graph API metadata, you can use extended properties and its REST API. You can verify which properties the metadata exposes at$metadata.

JSON representation

Here is a JSON representation of the resource

  "extensionName": "string",
  "id": "string (identifier)"


Property Type Description
extensionName String A unique text identifier for an open type data extension. Required.
id String A fully qualified identifier that concatenates the extension type with the extensionName. Read-only.




Method Return Type Description
Create openTypeExtension(in an existing resource instance), or a new contact, event, message, post, todoTask, or todoTaskList that contains an openTypeExtension object. Create an openTypeExtension object in an existing or new resource instance.
Get openTypeExtension Read properties and relationships of openTypeExtension object.
Update openTypeExtension Update openTypeExtension object.
Delete None Delete openTypeExtension object.