This is something that some OWASP project leaders have talked/tested in the past, so to try it I moved the current mailman-based O2 list to the new Google Groups (which look much better than a couple years ago)
My first step was to go to the mailman Subscribers page, get the 57 current subscribers:
... and feed them to the Direct Subscribe option using this welcome email:
... which only allowed 10 emails at the time, and required this captcha resolution
For reference here are my current settings/config:
The Group Type is Q&A forum
With this Group Options
