replyPUSH

Much like WordPress.com’s “Comment Reply via Email”, you can reply to any post you subscribe to.
Integrates with the wonderful <a href="https://wordpress.org/plugins/subscribe2/" title="subscribe2" rel="ugc">subscribe2</a> and <a href="http://replypush.com" title="replyPUSH.com" rel="nofollow ugc">replyPUSH.com</a> service to provide the email reply magic.
It automatically adds notifications for comment posts to keep the conversation flowing 🙂
All the subscriber need do, is reply at the top of their quoted email notification.

Reply By Email

Allows your users to reply to articles / blog posts and comments via email.

First versions of Absolute Comments implemented several features that are now, out of the box, part of WordPress.
Absolute Comments now simply adds a “Reply” link into comment notification emails, prefills the comment reply with the commenter’s name, and adds a few cute icons.
There’s no option or settings: just activate and forget it’s even a plugin.
Official page: <a href="http://planetozh.com/blog/my-projects/absolute-comments-manager-instant-reply/" title="Absolute Comments" rel="nofollow ugc">Absolute Comments</a>
Tip: To keep track of this plugin’s evolution and features, you are advised to subscribe to the <a href="http://planetozh.com/exit/feed" rel="nofollow ugc">author’s feed</a> or follow him on Twitter: <a href="http://twitter.com/ozh" rel="nofollow ugc">@ozh</a>

Ozh' Absolute Comments

Reply to comments from email notification

Reply By Email vs Ozh' Absolute Comments