Forum Email subscription Thread: No user is able to receive instant email notification.
 

On my forum instant email notification is not working. Users who have subscribed to a thread for email notification are not able to receive any mail when new post gets added to subscribed thread.

1) I have check database user gets successfully subscribed to a thread for email notification.
2) I am using SMTP server for sending mail, I have tested SMTP configuration from admin panel and received test mail successfully.

Please tell me what could be the issue or To debug this where should I start?

Thanks