Simulate 'Failed' response
I need to check case when email ( recipient ) does not exist.
I know you don't check if email address exists in real world, but you could allow to set one or some email address(es) in configuration
and send 'recipient not exist' response with appropriate status code when client/user sends email to that address(es)
Interesting idea! We will consider working on this feature once the request is in high demand. Thanks for the input!