You probably want to map a second email field which is why you're here today.
In SyncApps, we only use 1 primary email address as the basis of our unique data integration.
Mailchimp cannot house more than 1 email field for sending out emails as it's a factor of their system limitations.
A workaround is to map a second email field from CRM to a Mailchimp Text Field Merge tag yet that will not allow sending to it in Mailchimp as it only really allows for some automation if that field changes in any way.
If you have questions, don't hesitate to drop an email as we are available 24/7