We have a simple inbound/outbound email module, based on POP3/SMTP. It comes as an entire module with forms to use, though you can make your own of course. It is still in version 2.4 however so it would need some conversion. It's also not in the AppStore.
This isn't really a widget. A widget is a piece of javascript that is executed in the client.
If you want your application to be able to receive email, you are better off with a specific module.
Edit: See Bas' answer.