diff --git a/types/office-js-preview/index.d.ts b/types/office-js-preview/index.d.ts
index 32e3daf5d2..dc0269c7e2 100644
--- a/types/office-js-preview/index.d.ts
+++ b/types/office-js-preview/index.d.ts
@@ -16900,11 +16900,20 @@ declare namespace Office {
         /**
          * The email address of the owner of a shared item.
          */
-        owner: String;
+        owner: string;
         /**
-         * The remote REST URL related to the owner’s mailbox.
+         * The REST API's base URL (currently https://outlook.office.com/api).
+         * Use with targetMailbox to construct REST operation's URL.
+         * 
+         * Example usage: `targetRestUrl + "/{api_version}/users/" + targetMailbox + "/{REST_operation}"`
          */
-        restUrl: String;
+        targetRestUrl: string;
+        /**
+         * The target/owner's mailbox. Use with targetRestUrl to construct REST operation's URL.
+         * 
+         * Example usage: `targetRestUrl + "/{api_version}/users/" + targetMailbox + "/{REST_operation}"`
+         */
+        targetMailbox: string;
         /**
          * The permissions that the delegate has on a shared folder.
          */