Set a lead as non-marketing if they opt out of email marketing

Set a lead as non-marketing if they opt out of email marketing

I'm gathering Lead data via an enquiry form and wish to give them the option to opt out of marketing emails (which we send from Marketing Automation) whilst retaining the ability to send them non-marketing emails - so the email opt-out field doesn't work.  Is there anything built into Zoho CRM to do this - or do we need to use our own field?