As far as I've been able to figure out, you have to manually export & download your orders, format it into a CSV, upload the list as a new mailing list, and repeat before sending any new email to that list to catch any new orders/customers.
Squarespace does automatically create a new mailing list for any subscription product...or maybe only for members spaces...I don't recall exactly, but when I experimented with a subscription member space, it automatically created a mailing list for that group. So the functionality is in the system, but not currently able to be tied to a specific product purchase that is not a subscription.
I know coding this stuff is so much more difficult than us end-users realize. And this has been an issue for years and is really getting to be a dealbreaker between sticking with squarespace's all-in-one simplicity and switching to a separate email management system that can automate segmentation, etc. The current functionality is really lacking for online course creators.
