@August: the first sentence of your answer is truly right! But you don't need SMTP per user to achieve what Hamil wants. It is necessary to check if the user who wants to receive notifications is also assigned as follower for the corresponding topics. Given that you have configured your mail and notification system properly, of course.

Hi the mail configuration is far more complex than expected. please refer to these two posts with examples on\\ Zoho\ mail\\ and\ \Gmail\\&nbsp\;\.\ The\ module\ you\ may\ need\ is\ \SMTP Server per User which can be used for version 9