To verify multiple domains in Mailchimp and resolve DMARC/DKIM issues, each domain must be individually added, verified, and authenticated in your Mailchimp account. This typically involves accessing the Domains section in Mailchimp, clicking 'Authenticate', and following the instructions. This process includes adding CNAME and DKIM records to your domain's DNS settings. Tools such as MXToolbox and online DKIM validators can assist in identifying and resolving DNS record errors. Remember that each domain's reputation is managed independently, so it's vital to monitor deliverability metrics and address issues promptly for each domain. Proper authentication is crucial to maintain a good sending reputation, prevent deliverability problems, avoid spam and phishing, and enable segmentation of email marketing efforts across different brands or business units. Creating and configuring DMARC records correctly in your DNS settings tells receiving mail servers how to handle unauthenticated emails, helping to combat email abuse. Ignoring DMARC report issues that are unrelated to the Mailchimp configuration itself.