DummyNotificationGenerator

This app generates an original notification for your app proposal.
You can set title, message, large and small icons, and so on.

If you have own image file for large icon, app can pick your file in device.
(Since your image won't be resized, make it in an appropriate size)
If your device's OS is JellyBean or upper, app can generate notification with expanded style.

App can generate notifications with sound, LED flash and vibration, so you can simulate actual notifications.
You can set delay for notification generation in seconds... that will be able to pretend getting mails:D