diff --git a/pkg/identityserver/notification_registry_test.go b/pkg/identityserver/notification_registry_test.go
index 6aecddcfe2..fe1737eab8 100644
--- a/pkg/identityserver/notification_registry_test.go
+++ b/pkg/identityserver/notification_registry_test.go
@@ -15,6 +15,7 @@
 package identityserver
 
 import (
+	"fmt"
 	"testing"
 	"time"
 
@@ -98,3 +99,96 @@ func TestNotificationRegistry(t *testing.T) {
 		}
 	}, withPrivateTestDatabase(p))
 }
+
+// TestNotificationRegistryWithOrganizationFanout contains the test case for notifications that trigger the organization
+// fanout, validating the expected behavior. More details below.
+//
+// Base conditions:
+//   - Three users, the owner and two collaborators.
+//   - Two organizations, one with fanout and another without.
+//   - Two applications, one for each organization. The organization is the owner and admin/tech contact.
+//
+// Expected behavior:
+//   - Create notification for app-1 (no fanout). Only the owner should receive the notification.
+//   - Create notification for app2-2 (has fanout). Both the owner and collaborators should receive the notification.
+func TestNotificationRegistryWithOrganizationFanout(t *testing.T) {
+	t.Parallel()
+	p := &storetest.Population{}
+
+	usr1 := p.NewUser()
+	usr1Key, _ := p.NewAPIKey(usr1.GetEntityIdentifiers(), ttnpb.Right_RIGHT_ALL)
+	usr1Creds := rpcCreds(usr1Key)
+
+	usr2 := p.NewUser()
+	usr2Key, _ := p.NewAPIKey(usr2.GetEntityIdentifiers(), ttnpb.Right_RIGHT_ALL)
+	usr2Creds := rpcCreds(usr2Key)
+	usr3 := p.NewUser()
+	usr3Key, _ := p.NewAPIKey(usr3.GetEntityIdentifiers(), ttnpb.Right_RIGHT_ALL)
+	usr3Creds := rpcCreds(usr3Key)
+
+	org1 := p.NewOrganization(usr1.GetOrganizationOrUserIdentifiers())
+	org2 := p.NewOrganization(usr1.GetOrganizationOrUserIdentifiers())
+	org2.FanoutNotifications = true
+
+	// Register users as collaborators on both organizations.
+	for _, org := range []*ttnpb.Organization{org1, org2} {
+		org := org
+		for _, collab := range []*ttnpb.User{usr2, usr3} {
+			collab := collab
+			p.NewMembership(
+				collab.GetOrganizationOrUserIdentifiers(),
+				org.GetEntityIdentifiers(),
+				ttnpb.Right_RIGHT_ORGANIZATION_ALL,
+			)
+		}
+	}
+
+	// Sends notification to application's admin/tech contacts.
+	// Depending on the organization's fanout setting, the amount of receivers will vary.
+	app1 := p.NewApplication(org1.GetOrganizationOrUserIdentifiers())
+	app2 := p.NewApplication(org2.GetOrganizationOrUserIdentifiers())
+
+	a, ctx := test.New(t)
+	testWithIdentityServer(t, func(is *IdentityServer, cc *grpc.ClientConn) {
+		svc := ttnpb.NewNotificationServiceClient(cc)
+
+		for _, entityID := range []*ttnpb.EntityIdentifiers{
+			app1.GetIds().GetEntityIdentifiers(),
+			app2.GetIds().GetEntityIdentifiers(),
+		} {
+			entityID := entityID
+			res, err := svc.Create(ctx, &ttnpb.CreateNotificationRequest{
+				EntityIds:        entityID,
+				NotificationType: "test_notification",
+				Receivers: []ttnpb.NotificationReceiver{
+					ttnpb.NotificationReceiver_NOTIFICATION_RECEIVER_ADMINISTRATIVE_CONTACT,
+					ttnpb.NotificationReceiver_NOTIFICATION_RECEIVER_TECHNICAL_CONTACT,
+				},
+			}, is.WithClusterAuth())
+			if a.So(err, should.BeNil) && a.So(res, should.NotBeNil) {
+				a.So(res.Id, should.NotBeZeroValue)
+			}
+		}
+
+		// Validates the amount of notifications received by each user.
+		for _, tt := range []struct {
+			userID             *ttnpb.UserIdentifiers
+			notificationAmount int
+			creds              grpc.CallOption
+		}{
+			{userID: usr1.GetIds(), notificationAmount: 2, creds: usr1Creds},
+			{userID: usr2.GetIds(), notificationAmount: 1, creds: usr2Creds},
+			{userID: usr3.GetIds(), notificationAmount: 1, creds: usr3Creds},
+		} {
+			tt := tt
+			ttName := fmt.Sprintf("Expect %s to have %d notifications", tt.userID.GetUserId(), tt.notificationAmount)
+			t.Run(ttName, func(t *testing.T) { // nolint:paralleltest
+				a, ctx := test.New(t)
+				list, err := svc.List(ctx, &ttnpb.ListNotificationsRequest{ReceiverIds: tt.userID}, tt.creds)
+				a.So(err, should.BeNil)
+				a.So(list, should.NotBeNil)
+				a.So(list.Notifications, should.HaveLength, tt.notificationAmount)
+			})
+		}
+	}, withPrivateTestDatabase(p))
+}