No user data or any other data related to Do It Later will ever be sold or made available to third parties. With Do It Later, what happens on your device stays on your device.
Do It Later does not send any data, anywhere, unless it is requested by the user (e.g. sending an automatic SMS.)
Do It Later can make use of your Google Gmail account (if granted access) to send emails on your behalf via the send email action. Do It Later will never use this access to send emails other than those configured by the user (using the send email action). Aside from the usage described, Do It Later will not access, store or share any Google user data or account information.
No user data or any other data related to Do It Later will ever be sold or made available to third parties.
Do It Later will never include any third party services whose purpose is to monetize user data in any way.