From http://support.atlassian.com/browse/JSP-1078

Essentially have configurable a challenge / response to issue creation in the POP service:

Michael Czeiszperger:
I'm finishing the email gateway, and couldn't find a solution to this dilemma. I'd like users to continue to be able to send email to support@address.com, but that address is being innundated with spam. Incredible amounts of spam. I configured a JIRA email gateway with createusers=false so that spam wouldn't be sucked into JIRA, and only legimate users could create issues. The problem is we don't current require users to be registered, so when we switch this on email to support@address.com from existing users both won't create issues and the user will never be notified of that fact.

So, is there any way of sending email to someone who's not in the system who hits a PopService handler with createusers=false?