Google and Yahoo are enforcing new requirements for email authentication starting from February 2024. These changes aim to protect recipients from unwanted emails by requiring senders to properly authenticate their emails using DKIM, SPF, and DMARC. Senders who don't comply with these best practices may face issues getting their emails delivered in the inbox. To ensure compliance, Postmark recommends that customers take five steps: understanding their domains' authentication status, authenticating their mail with custom DKIM and SPF, setting up DMARC, registering their domain for Google Postmaster Tools, and keeping spam complaint rates under 0.3%. The changes primarily target large bulk senders, but transactional senders are also expected to comply with enhanced deliverability and engagement requirements.