Open the account menu, click Settings, then choose Email Defaults. Everything here is under "Automatic notifications" — sent to your own login email, not to clients, except the first one below:
- Send clients an automatic thank-you email after they pay — this one goes to the client, not you.
- Email me when a client makes a payment
- Email me when someone comments on an invoice or estimate
- Send me a weekly activity summary
Toggle whichever you want on or off, then click Save changes.
You can customize the wording of each email from the Email type dropdown further up the page, including the payment reminder. Due date reminders themselves — which emails go out before and after an invoice is due — are set on Invoice Defaults now, next to your payment terms: see Payment terms and reminders.