Web-based online discussion tool (forum) that supports post from email

Question

I'm looking for a web-based tool (ideally self-hosted) that:

Must have:

• Online threaded discussions (similar to Facebook comments)
• Integration with email, so people can follow topics and join the discussion from email (similar to most helpdesk tools)

Nice to have:

• Is a WordPress plugin
• Offers iPhone and Android apps
• Integration with Facebook groups so people can join the discussion from a Facebook group (not sure if this is even technically possible)

Answer 1

How about EasyDiscuss https://extensions.joomla.org/extension/easydiscuss/ for Joomla which has threads and email integration along with posting to Facebook & Twitter.