For the wizard: it’s okay if the wizard doesn’t display the failure. However, it should also not indicate that the email was sent successfully. Something closer to truth would be more helpful. If it’s too difficult to show the return status, it would be better to say, “registration email successfully added to the queue. check /path/to/log for status.”
For the log: The worker thread should log the status, especially when there’s an error. I’m not familiar with the architecture, but I don’t see anything useful in “unicorn.stderr.log” or anywhere else. Something must be gobbling the return code and error message…