DMARC loop detection signifies a recurring issue where failure reports are sent to a mailbox also subject to DMARC policies, creating an endless cycle. Resolution involves setting up a dedicated reporting mailbox without DMARC enabled, actively monitoring DMARC reports, ensuring DNS records have valid syntax, and avoiding support inboxes for DMARC reports. Temporary issues and nameserver problems might be initial indicators, but proper configuration and continuous oversight are essential.