VMC and CMC Certificates for BIMI: How to Choose, Buy and Deploy
Complete guide to obtaining and deploying a VMC or CMC certificate: CA comparison, pricing, prerequisites and free hosting.
Email protocols, configuration, and best practices for reliable messaging.
54 articles
April 2026
March 2026
Understanding email headers: the complete guide to reading and analyzing every field
Every email carries an invisible logbook. This guide teaches you how to extract it, read it field by field, and diagnose deliverability or security issues.
10 email filter gaps: the subtle header signals your gateway misses
Your email gateway blocks 99% of threats. But the 1% that gets through is what matters. Here are the 10 header indicators that most filters ignore.
Test Email Deliverability: The Complete Guide Before Sending
One in five emails never reaches the inbox. This guide shows you how to test your email deliverability before sending and fix every issue.
DMARCbis: the complete guide to understanding and migrating to the new DMARC standard
DMARCbis replaces RFC 7489, drops the PSL in favor of the DNS Tree Walk, adds three tags and splits reporting into three documents. This guide covers everything: how it works, migration, compliance.
BIMI Without a VMC: The Budget-Friendly Guide to Displaying Your Logo in the Inbox
BIMI isn't just for large enterprises. This guide covers the 3 deployment tiers (free, CMC, VMC), the DNS prerequisites, and 5 steps for small and mid-sized businesses.
SVG Tiny-PS: understanding the security profile required by BIMI
An SVG file can contain JavaScript, phishing links and tracking pixels. Learn how the SVG Tiny-PS profile neutralizes these threats to secure BIMI logos.
February 2026
End of Basic Auth SMTP on Microsoft Exchange Online: timeline, 550 5.7.30 error, and migration guide
Microsoft is retiring Basic authentication for SMTP AUTH on Exchange Online. Revised timeline, 550 5.7.30 error, OAuth alternatives, HVE, Graph API, and step-by-step migration checklist.
Port 25 blocked: diagnosis and solutions by hosting provider
Port 25 is blocked by most cloud providers and ISPs to fight outbound spam. Here's how to diagnose the block and restore your sending capability.
STARTTLS, SSL/TLS and SMTP: which encryption for your emails?
SSL, TLS, STARTTLS, Implicit TLS, DANE, MTA-STS: email encryption in transit relies on mechanisms that are often confused. This guide clarifies each protocol, explains their vulnerabilities, and shows how to configure robust TLS encryption on Postfix, Exim and Exchange.
SMTP ports explained: 25, 465, 587, 2525, which one should you use?
Port 25, 465, 587, or 2525? Each SMTP port has a specific role. This guide breaks down how each port works, its encryption method, the relevant RFCs, and helps you pick the right port for your use case.
How to test the SMTP connectivity of your MX servers
Your DNS records are perfect, but emails aren't getting through? The problem might be at the transport layer. This guide shows you how to test SMTP connectivity for each MX server, step by step.
Set up TLS-RPT: step-by-step guide for Microsoft 365, Google Workspace, and OVHcloud
Hands-on tutorial to set up TLS-RPT (SMTP TLS Reporting) on Microsoft 365, Google Workspace, and OVHcloud. DNS record, verification, and troubleshooting included.
Configure MTA-STS for Microsoft 365 and Google Workspace
Step-by-step tutorial to deploy MTA-STS on Microsoft 365, Google Workspace, and Cloudflare. MX patterns, policy file, hosting, and validation included.
Spamhaus vs Barracuda vs SpamCop: Complete Email Blocklist Comparison
Detailed comparison of the 3 main email blocklists: detection methods, false positive rates, delisting procedures, and impact on Gmail, Outlook, and Yahoo deliverability.
Why Your Emails End Up in Spam: The Complete Diagnostic Guide
Are your emails consistently landing in spam? This guide analyzes the 5 main causes and gives you a concrete action plan to restore optimal deliverability.
How to Remove Your IP from a Blacklist: The Complete Delisting Guide
Is your IP on a blacklist and your emails getting rejected? This guide details the delisting procedures for each major blacklist, including processing times and best practices to avoid getting listed again.
January 2026
Twilio SendGrid: Complete Technical Guide for Transactional Email
A detailed technical guide for developers: DNS configuration (SPF, 2048-bit DKIM), Web API v3, SMTP Relay, dedicated vs shared IP, limits and webhooks.
December 2025
BIMI, VMC, CMC: compatibility and DNS prerequisites (Gmail, Yahoo, Apple Mail)
Putting your logo in the inbox: what you actually need to configure in DNS for BIMI, and how to choose between VMC and CMC.
Gmail/Yahoo one-click unsubscribe: what RFC 8058 changes and how to implement it
Gmail and Yahoo require a one-click unsubscribe via RFC 8058-compliant List-Unsubscribe headers. Here's the expected format, the server-side POST, and the compliance checklist.
Gmail ends POP fetching from other accounts in 2026: impact and action plan
Starting January 2026, Gmail will no longer continuously fetch messages from external mailboxes via POP ("Check mail from other accounts"). Impacts, timeline, and alternatives for Gmail and Google Workspace users and admins.
November 2025
Behind the scenes of the CaptainDNS MCP
How we wired CaptainDNS to AIs through MCP: architecture, HTTP+SSE transport, JSON-RPC, 424 errors, timeouts, and what we learned along the way.
BIMI logo cache: run a brand refresh and make the new logo show up everywhere
Your logo changed but inboxes still display the old one? It is not only a DNS issue: mailbox providers cache BIMI assets. Discover how the cache layers work and how to plan a smooth BIMI migration.
Gmail tightens its sending rules: what's changing for senders starting November 2025
Starting in November 2025, Google enforces new security requirements for bulk senders: full SPF/DKIM/DMARC authentication, TLS encryption and strict unsubscribe management.
October 2025
