val inbox : unit -> t list
inbox () returns the content of the development in-memory mailbox. Intercepted emails land here, they can be used during testing to make sure that certain emails were sent.
clear_inbox () removes all the emails from the development in-memory mailbox. A subsequent call on `inbox ()` will return an empty list.
send ?ctx email sends the email
bulk_send ?ctx emails Sends the list of emails
emails. If sending of one of them fails, the returned Lwt.t fails.