Simple Machines Forums has a somewhat hidden feature that many popular forums use which emails members when a post they engaged in is updated.
There is a universal setting you can adjust so that Members are emailed when there are any updates to a topic they posted or replied to.
This is a great way to remind people to return to the forum and keep them updated when something they cared about has new posts.
In SMF 2.x, you can do this by clicking Admin and going to Configuration >> Themes and Layout >> Member Options >> then scroll down to find your current theme and click “Change current options for all members using this theme”
Then next to “Turn notification on when you post or reply to a topic” click the dropdown on the left and select “Change,” then click the box to the right to select it, then click “Save” at the bottom.
Now you should inform your members about the change, first by mentioning it in a post and also explaining that if anyone wants to turn it off they can do so in their Profile under the Notification settings.
Then in your Admin section to Members >> Registration >> Registration Agreement and update the agreement to reflect this new setting.
For example, just add something like: “The forum may send email notifications when someone updates a topic you participated in to keep you updated on the topic. You can turn this off anytime in your profile’s notification settings.”
Here’s more on engaging and growing your forum community.