How do I makesure a Lead does not receive any emails through the CRM email function and the Campaigns add on?

How do I makesure a Lead does not receive any emails through the CRM email function and the Campaigns add on?

How do I makesure a Lead does not receive any emails through the CRM email function and the Campaigns add on?

Usually through campaigns I would add to 'DO NOT MAIL' list but is this synced with the emails sent out through the CRM?