In phpBB3, topic reply notification is set to “Off” by default. Unlike vBulletin, where you are automatically subscribed to threads which you reply to, in phpBB, you have to manually check “Notify me when a reply is posted” from the “Post reply” page to subscribe.
However, there is an easy file edit that will keep “Notify me when a reply is posted” checked by default when posting a reply.
Open ‘includes/functions_user.php’:
Find :
[code language=”php”] ‘user_notify’ => 0,[/code]
Replace with :
[code language=”php”] ‘user_notify’ => 1,[/code]
After this edit, users will be automatically subscribed to threads while replying.