diff --git a/components/calendar/calendar-sidebar-panel.tsx b/components/calendar/calendar-sidebar-panel.tsx
index 7c22a2f5..4d0c7987 100644
--- a/components/calendar/calendar-sidebar-panel.tsx
+++ b/components/calendar/calendar-sidebar-panel.tsx
@@ -144,6 +144,12 @@ export function CalendarSidebarPanel({
           {cal.id === BIRTHDAY_CALENDAR_ID && (
             <Cake className="w-3 h-3 text-muted-foreground flex-shrink-0" />
           )}
+          {!cal.isShared && Object.keys(cal.shareWith || {}).length > 0 && (
+            <Users
+              className="w-3 h-3 text-muted-foreground flex-shrink-0 ml-auto"
+              aria-label={tMgmt('share')}
+            />
+          )}
         </button>
       </div>
     );
diff --git a/components/contacts/contacts-sidebar.tsx b/components/contacts/contacts-sidebar.tsx
index 328ef384..07afccf1 100644
--- a/components/contacts/contacts-sidebar.tsx
+++ b/components/contacts/contacts-sidebar.tsx
@@ -685,7 +685,13 @@ function AddressBookItem({
     >
       <Book className="w-4 h-4 flex-shrink-0" />
       <span className="truncate">{book.name}</span>
-      <span className="ml-auto text-xs text-muted-foreground tabular-nums">
+      {!book.isShared && Object.keys(book.shareWith || {}).length > 0 && (
+        <Users className="w-3 h-3 text-muted-foreground flex-shrink-0 ml-auto" />
+      )}
+      <span className={cn(
+        "text-xs text-muted-foreground tabular-nums",
+        !(!book.isShared && Object.keys(book.shareWith || {}).length > 0) && "ml-auto"
+      )}>
         {contactCount}
       </span>
     </button>
diff --git a/components/settings/address-book-management-settings.tsx b/components/settings/address-book-management-settings.tsx
index 668307a8..ef0c37b0 100644
--- a/components/settings/address-book-management-settings.tsx
+++ b/components/settings/address-book-management-settings.tsx
@@ -139,6 +139,19 @@ export function AddressBookManagementSettings() {
             {t("default")}
           </span>
         )}
+        {(() => {
+          const shareCount = Object.keys(book.shareWith || {}).length;
+          if (shareCount === 0 || book.isShared) return null;
+          return (
+            <span
+              className="flex items-center gap-1 text-xs text-muted-foreground bg-muted px-2 py-0.5 rounded-full"
+              title={t("share")}
+            >
+              <Users className="w-3 h-3" />
+              {shareCount}
+            </span>
+          );
+        })()}
         <div className="flex items-center gap-1 opacity-0 group-hover:opacity-100 transition-opacity">
           {canRename && (
             <button
diff --git a/components/settings/calendar-management-settings.tsx b/components/settings/calendar-management-settings.tsx
index e28d76d9..5cf4d417 100644
--- a/components/settings/calendar-management-settings.tsx
+++ b/components/settings/calendar-management-settings.tsx
@@ -516,6 +516,20 @@ export function CalendarManagementSettings() {
                 </span>
               )}
 
+              {(() => {
+                const shareCount = Object.keys(cal.shareWith || {}).length;
+                if (shareCount === 0 || cal.isShared) return null;
+                return (
+                  <span
+                    className="flex items-center gap-1 text-xs text-muted-foreground bg-muted px-2 py-0.5 rounded-full"
+                    title={t('share')}
+                  >
+                    <Users className="w-3 h-3" />
+                    {shareCount}
+                  </span>
+                );
+              })()}
+
               <div className="flex items-center gap-1 opacity-0 group-hover:opacity-100 transition-opacity">
                 <button
                   type="button"
diff --git a/lib/jmap/client.ts b/lib/jmap/client.ts
index 0bce1a2b..ff2c8183 100644
--- a/lib/jmap/client.ts
+++ b/lib/jmap/client.ts
@@ -3079,11 +3079,19 @@ export class JMAPClient implements IJMAPClient {
   }
 
   private contactUsing(): string[] {
-    return ["urn:ietf:params:jmap:core", "urn:ietf:params:jmap:contacts"];
+    const using = ["urn:ietf:params:jmap:core", "urn:ietf:params:jmap:contacts"];
+    if (this.hasCapability("urn:ietf:params:jmap:principals")) {
+      using.push("urn:ietf:params:jmap:principals:owner");
+    }
+    return using;
   }
 
   private calendarUsing(): string[] {
-    return ["urn:ietf:params:jmap:core", "urn:ietf:params:jmap:calendars"];
+    const using = ["urn:ietf:params:jmap:core", "urn:ietf:params:jmap:calendars"];
+    if (this.hasCapability("urn:ietf:params:jmap:principals")) {
+      using.push("urn:ietf:params:jmap:principals:owner");
+    }
+    return using;
   }
 
   private getCalendarCapableAccountIds(): string[] {