Migrating to a new ESP under Google and Yahoo's updated sender requirements necessitates careful attention to several key areas, including sender reputation, IP warming, email authentication (SPF, DKIM, DMARC), and list hygiene. A successful migration involves configuring DNS records, warming up the new IP address gradually, cleaning your email list, and continuously monitoring deliverability metrics, often using tools like Google Postmaster Tools. Experts recommend a strategic approach to IP warming and suggest using a dedicated subdomain to isolate sending reputation. Adhering to authentication standards and implementing a robust DMARC policy are critical for protecting your domain's reputation and ensuring compliance. There are mixed opinions on running both ESPs simultaneously, with some advocating for a clean cut while others question that recommendation. Failing to address these areas can lead to deliverability issues and non-compliance with the new enforcement rules.