This error is near impossible for anyone but Mailchimp to resolve. For example, it is impossible to know which email addresses Mailchimp has sent to in the past; how can anyone but Mailchimp then identify which email addresses have ‘never been sent through their systems’? To resolve the issue, do what it says in the error message and email Mailchimp.
Looks like there’s a problem
Review the feedback below before sending your campaign.
Mailchimp’s artificial intelligence system, Omnivore, has identified some issues with the addresses on Subscribers that have never been sent to through our system.
Omnivore has indicated that these addresses may cause high abuse complaints or bounce rates, and could contain spamtrap addresses. These are serious issues when it comes to email marketing and delivery. The issues with these addresses will need to be resolved before the list can be sent to.
To move forward, please review these addresses to determine if they need to be reconfirmed, or removed from the list. If you recently imported some new addresses to an existing list, you can undo your recent imports from your import history page. You may also contact our compliance team at firstname.lastname@example.org for further insight into what may be causing this detection.