Use Replyable as the best free subscribe to comments experience for WordPress.
But for as little at $2.99 a month it can be so much more.
Plans and Pricing
Replyable comment subscriptions with guaranteed delivery
Comment subscriptions for site visitors
Beautiful email templates
Subscriptions are automatically paused and users are alerted after 4 comments per hourAutomatic throttling of chatty conversations +
Send a new comment right from your inbox, online or off
Turn emails into comments - like magic
post and conversation recaps that let the user reply to any comment in the conversation from emailEnhanced templates for increased replyability +
Moderation & Comment Tools for Busy Authors & Multi-Author Sites
All Conversation Starter Features
Let your authors reply to and moderate their own comments without ever touching WordPressAutomatic subscriptions for authors and guest authors +
Simple email commands for moderating commentsShare the workload with email-based moderation for authors +
Keep conversations going for increased SEO and search relevancy
Intelligent comment subscriptions for any size community
All Daily Discourse Features
We check comments for relevance and reading level - and only email the best onesSmart algorithms make sure nobody gets too much email +
If a post gets too busy we'll send a daily digest of new comment activity instead of wrecking inboxesScales easily to posts with thousands of comments per day +
Daily recaps of comment activity
After installing Replyable you can upgrade directly from your WordPress dashboard in the Settings > Replyable screen.