Not the email I want to send. OSSN private message to everyone the same at once.
Just a thought... You can use the Feedback component from OpenTeknik available at https://www.openteknik.com/product/view/5857/feedback to ask a question sitewide. You will have to alter it some to ask a question, but it should suffice for the moment, Aside from this you can use PhpList available at https://phplist.com to send a mass email message to the users list you can get by using the Users Export component found at https://www.opensource-socialnetwork.org/component/view/850/users-export-csv. Worked well for me.