What is a Single Opt-In user in Vtiger CRM?

A Single Opt-In user is a contact who is automatically subscribed to receive marketing emails immediately upon being added, without needing to confirm their subscription via email.

• Single Opt-In (User): Set manually by a user when the contact agrees to receive marketing emails, or automatically when a contact is created.
• Single Opt-In (Web Form): Set automatically when a contact submits a web form with the email marketing checkbox selected.