To only receive emails from your subscribers to your Substack email address (firstname.lastname@example.org), follow these two steps.
1. Head to your Settings page and click on Basics in the left navigation bar. Scroll to "Receive email replies to your posts from".
2. Select "All subscribers" from the dropdown box.
Why would I change my settings?
If your email replies setting is currently set to "Everyone", then anyone can email you at your @substack.com author alias.
There have been instances of email alias spoofing in which a spammer can send a message using your @substack.com author alias (to a list of non-subscriber addresses the spammer has acquired outside of Substack). If you have your setting set to "Everyone", you may receive email replies from non-readers to a spam email that was sent by a spammer.