DMARCbis Is Published: What RFC 9989 Changes
After eleven years, DMARC is a real standard: RFC 9989, 9990, and 9991 replace RFC 7489. What is different, what stays, and the short list of actions for senders.
Authentication
Explore authentication technologies used in modern communication systems, including SPF, DKIM, DMARC, multi-factor authentication, OTP verification, sender authentication, passkeys, trust validation, and identity verification flows.
Microsoft's Rejection Phase Is Live: A 550 5.7.515 Field Guide
Outlook now hard-rejects non-compliant bulk mail with 550 5.7.515, and Safe Senders cannot override it. Diagnosing the bounce and fixing the authentication behind it.
2025 in Email: The Year Authentication Became Mandatory Everywhere
Microsoft joined the mandate, Gmail moved to hard rejection, and DMARCbis reached the finish line. What 2025 changed for senders and what it sets up for 2026.
DMARCbis: What Changes When DMARC Gets a New RFC
DMARCbis is finishing its journey through the IETF, replacing RFC 7489 with a Standards Track spec. The tree walk, retired tags, and what senders should do now.
SPF's 10-Lookup Limit: Includes, Flattening, and Permerror
Every include, a, mx, and redirect in your SPF record costs a DNS lookup, and the budget is ten. Why records break at scale and how to fix them without flattening regret.
Microsoft's New Outlook Sender Requirements: A Compliance Guide
Microsoft now requires SPF, DKIM, and DMARC from high-volume senders to Outlook consumer domains. What the rules demand, how enforcement works, and how to comply.
Parsing DMARC Aggregate Reports: From Raw XML to Decisions
RUA reports arrive as gzipped XML that nobody reads by hand. The report anatomy, a working parsing pipeline, and how to interpret the sources you will find.
DKIM Replay Attacks: How Spammers Weaponize Your Valid Signatures
A DKIM signature stays valid no matter who forwards the message. How replay attacks abuse that property to spend your reputation, and the defenses that limit the damage.
Yahoo and Gmail's February 2024 Bulk Sender Requirements: A Compliance Checklist
The complete compliance checklist for Yahoo and Gmail's February 2024 bulk sender requirements. Authentication, unsubscribe, complaint rates—what you actually need.
The ARC Header: How Forwarding Breaks DMARC and What You Can Do
Forwarders break DMARC by modifying messages in transit. ARC (RFC 8617) preserves authentication results across hops. How it works, who supports it, and the limits.
BIMI Explained: Is the VMC Investment Worth It for B2B Senders?
BIMI displays your logo in supporting inboxes. The VMC certificate costs $1,500/year. Whether the brand recognition lift justifies the spend honestly assessed.
Understanding DMARC Policies: From p=none to p=reject Without Breaking Things
How to move from DMARC p=none to p=reject without breaking production mail. The phased rollout that actually works with the failures most senders hit.