Google Contacts, the address book built into Gmail, lets you keep track of all your contacts, see when you last interacted with them, and more.
Add valid email submissions to the table and reply with their IDs.
Turn emailed entry requests into database rows, with a reply that confirms the ID or tells the sender what to fix.
Add valid customers and update existing entries by ID.
See new and changed customers in your list, plus a report of entries needing your review after a JSON export.