Email Authentication for Developers: SPF, DKIM, DMARC, BIMI, and MTA-STS in 2026
Microsoft started rejecting unauthenticated bulk email in May 2025. This is the developer's guide to SPF, DKIM, DMARC, BIMI, and MTA-STS -- with real DNS records, a rollout strategy, and tools to verify everything.
DevToolLab Team· 
