Yes, it has both options.

Zoho Discussions has 'Follow this Topic' option to receive emails on the discussions you are follow.

To post to Zoho Discussions directly from your email, it has Email2Forum option. More details on this are available here.

http://help.discussions.zoho.com/forum-settings.html#Email2F...

https://forums.zoho.com/topic/explain-email2forum-feature%3F

Ofcourse, these features can be made available for free for open source projects.