When you post a new note, subscribers will not get an email as they would do with newsletters.
For the web:
Subscribers and followers can receive a notification in their activity bell with new notes. This can be disabled in their Substack account Settings page in the Connections section. To stop receiving notes notifications, subscribers and followers can uncheck the "Email" and "Push" boxes next to "New notes".
For the Substack app:
We'll send your subscribers and followers a one-time push notification when you publish your first note. We may also send them push notifications for notes they haven’t seen but push notifications won't be sent for every note you publish.
Subscribers and followers can disable push notifications for new notes by signing into their Substack account on the web and disabling "New notes" notifications on their account Settings page.