How do matching rules work?

Matching rules, by default, work by matching a Mailchimp audience member to a Salesforce contact or lead using the standard email address field. If a duplicate is found, we will use both the first name and the last name.  Finally, we will use the most recently modified record. 

If you have additional email fields on the Salesforce contact or lead object, you can choose to map to these fields as well. Simply click on the dropdown next to the email - https://jmp.sh/HEZOMWl1