Fixing a low IP and domain reputation with a high spam rate requires a multifaceted approach focused on improving authentication, engagement, and list hygiene. Key steps include implementing SPF, DKIM, and DMARC authentication, cleaning email lists to remove unengaged subscribers, warming up IP addresses gradually, and monitoring sender reputation using tools like Google Postmaster Tools and Microsoft SNDS. It's crucial to analyze spam complaints, avoid spam trigger words, segment email lists based on engagement, and use email verification services to minimize bounce rates. Consistent action and adherence to best practices are essential for long-term improvement.