Hey @Nina_11
I think the original topic was honestly about a different problem, the OP was suggesting that replies were being sent directly via email, rather than back to the Discourse site. Discourse never discloses the email address of other users, so it’s not possible from a technical perspective.
Assuming you want to stop email replies appearing in Discourse though, the setting is called reply by email enabled. Uncheck the box and replies will no longer be routed back to their respective topics.
Email sent after that switch is toggled will no longer tell the user that response by email is an option, but if your users have already gotten into that habit you may want to also announce the change.