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.
Protocols
Technical analysis of the protocols powering digital communication, including SMTP, IMAP, SIP, XMPP, RCS, WebRTC, MMS, and emerging standards that define how modern messaging and communication systems operate.
Subaddressing: What Plus Addresses Tell Senders
user+anything@gmail.com is one mailbox wearing labels. How subaddressing works, why blocking it backfires, and what plus addresses reveal about your data flows.
Greylisting, Tarpitting, and Other Receiver Defenses Senders Should Understand
Receiving servers defend themselves with deliberate delays, temporary rejections, and traps for impatient senders. How each defense works and how a good MTA passes them.
Email Address Internationalization: SMTPUTF8 and EAI in Practice
Addresses like 佐藤@例え.jp are valid email. How EAI and SMTPUTF8 work, who supports them, and what sending systems break when a Unicode address shows up.
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.
Email Header Forensics: Reading Received Chains and Authentication-Results
Every delivery question has its answer in the headers. How to trace a message's path through Received lines and decode Authentication-Results like a postmaster.
TLS-RPT: The Reporting Layer Your MTA-STS Deployment Is Missing
TLS-RPT delivers daily JSON reports on every failed TLS negotiation to your domain. The record, the report format, and how to turn failures into fixes.
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.
Why DMARC Alignment Matters More Than DMARC Itself
DMARC fails when SPF or DKIM pass for the wrong domain. The alignment rules, relaxed vs strict modes, and the ESP configuration that fixes it.
DKIM Key Rotation: A Practical Guide for Production Environments
How to rotate DKIM keys in production without breaking signatures. Dual-selector strategy, 2048-bit key sizes, and the rotation cadence that actually works.
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.