A unique profile ID must be added to all links in your emails, so we can identify a person when he visits your website from an email.
After you connect the Mailchimp channel in Datatrics you have to select the box "E-commerce link tracking" in Mailchimp. You can find this in the Settings & Tracking section in the Campaign Builder as shown in the image below:
That's it! Datatrics will now identify visitors as MailChimp users when they visit your website from an email and also when the revisit. All (anonymous) historical events will also be added to the user/customer.