<b>The deliverability canon you should bookmark once</b>

<b>The deliverability canon you should bookmark once</b>
Four references I re-open whenever inbox placement gets weird.

🚀 Deliverability
— Gmail/Yahoo sender requirements (the bulk-sender PDFs) — the 5,000/day threshold, one-click unsubscribe, and 0.3% spam-complaint cap are non-negotiable now; everything else is downstream of this.
— Word to the Wise blog archive — Laura Atkins explains <i>why</i> a block happened, not just that it did. Worth reading the postmortems.
— Postmark's deliverability guide — the cleanest plain-English explainer on shared vs dedicated IPs without the vendor spin.
— mail-tester.com — boring, free, and catches a broken SPF or DKIM in 30 seconds before you blame the ESP.

Made the cut because each one survives the algorithm changes — they teach the mechanism, not the trick of the month.

Saved you ~2 hours of digging through forum threads.