diff --git a/change/@microsoft-teams-js-d0373412-a60a-4bee-8468-77ff80125588.json b/change/@microsoft-teams-js-d0373412-a60a-4bee-8468-77ff80125588.json
new file mode 100644
index 0000000000..2db42105d6
--- /dev/null
+++ b/change/@microsoft-teams-js-d0373412-a60a-4bee-8468-77ff80125588.json
@@ -0,0 +1,7 @@
+{
+  "type": "none",
+  "comment": "Updated documentation on IDs for `mail` and `calendar` capability",
+  "packageName": "@microsoft/teams-js",
+  "email": "vikramtha@microsoft.com",
+  "dependentChangeType": "none"
+}
diff --git a/packages/teams-js/src/public/calendar.ts b/packages/teams-js/src/public/calendar.ts
index d10fe4e033..64a686b174 100644
--- a/packages/teams-js/src/public/calendar.ts
+++ b/packages/teams-js/src/public/calendar.ts
@@ -84,7 +84,11 @@ export namespace calendar {
 
   /** Open calendar item parameters. */
   export interface OpenCalendarItemParams {
-    /** An unique base64-encoded string id that represents the event's unique identifier of the calendar item to be opened. */
+    /** An unique base64-encoded string id that represents the itemId or messageId.
+     * The only acceptable id for this itemId is the EWS (Exchange Web Services) ID. However,
+     * if you are using Graph API, you must convert the REST ID to a EWS ID. The conversion is done by
+     * replacing "+" characters with "-" and "/" characters with "_".
+     */
     itemId: string;
   }
 
diff --git a/packages/teams-js/src/public/mail.ts b/packages/teams-js/src/public/mail.ts
index 945d56a2fb..0e98fa067d 100644
--- a/packages/teams-js/src/public/mail.ts
+++ b/packages/teams-js/src/public/mail.ts
@@ -74,7 +74,11 @@ export namespace mail {
 
   /** Defines the parameters used to open a mail item in the user's mailbox */
   export interface OpenMailItemParams {
-    /** An unique base64-encoded string id that represents the itemId or messageId. */
+    /** An unique base64-encoded string id that represents the itemId or messageId.
+     * The only acceptable id for this itemId is the EWS (Exchange Web Services) ID. However,
+     * if you are using Graph API, you must convert the REST ID to a EWS ID. The conversion is done by
+     * replacing "+" characters with "-" and "/" characters with "_".
+     */
     itemId: string;
   }