If you want to get email notifications when someone posts to a topic you’re “watching,” do this:
Click on your profile icon in the upper right corner:
Select Settings. Scroll to the bottom of the Settings page. There’s a section called Email.
Check the box for “Send an email when replies are made to topics I am subscribed to.” Then click the Save Changes button.To confirm that you're watching (subscribed to) a topic
Click on the topic title to open it.
You'll know you’re subscribed to that topic if one of the menu buttons says “Watching."
Also, when you open the button menu the “Watching” bell is checked: