... concrete. Google and Yahoo rolled out new requirements for senders pushing more than 5,000 emails per day: SPF, DKIM, and DMARC became mandatory, one-click unsubscribe was required, and spam complaint rates had to stay below 0.10% in Postmaster Tools. Cross 0.30% and your mail gets rejected outright. From November 2025, Gmail tightened enforcement further. That's what makes this a tax rather than a fee. Google and Microsoft don't just host your inbox and your customers' inboxes ... ... DKIM, DMARC, opt-in subscribers, quality informational content, sent regularly. Then a few months ago they sent an important update after a six-month hiatus. Open rate: less than 10%. The audit revealed their domain reputation in Google Postmaster