To find the unique Mailchimp Campaign ID in an email, click “View Full Headers” in your email application. Since every email application is different, you might have to refer to your help files. Usually, if you do a search for “full email headers” or “full message headers,” you’ll find the instructions you need.
The Campaign ID contains information that allows our system to instantly remove you from the sender’s list, but we don’t tell the sender that you complained. It also sends an alert to our abuse desk, so we can investigate the sender.
The image below shows where the Campaign ID is located when a campaign’s full headers are displayed: