Articles - Page 5

March 2026

Diagram of the SPF 10 DNS lookup limit with a mechanism counter for include, a, mx, and redirect

CaptainDNS · March 3, 2026

SPF "Too Many DNS Lookups": The Complete Guide to Fixing the 10 Lookup Limit

Diagnose and fix the SPF "too many DNS lookups" error: how lookups are counted, what causes the limit to be exceeded, and 5 methods to stay within the limit of 10.

Diagram of the three BIMI deployment tiers for an SMB: self-asserted, CMC, and VMC

CaptainDNS · March 2, 2026

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.

CaptainDNS · March 2, 2026

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

CaptainDNS · February 28, 2026

BIMI logo: create a compliant SVG Tiny-PS file in 4 steps

A regular SVG file won't work for BIMI. This guide explains how to create, convert, and validate a compliant SVG Tiny-PS file.

Diagram of an email rejected by Gmail with 550 5.7.26 and UsernameCaseMapped errors

CaptainDNS · February 26, 2026

Gmail 550 5.7.26 and UsernameCaseMapped rejections: causes, diagnosis, and fixes

Gmail rejecting your emails with 550 5.7.26 or UsernameCaseMapped? Technical causes, step-by-step diagnosis, and SPF/DKIM/DMARC fixes to resolve these permanent bounces.

DNSSEC SERVFAIL diagnosis: decision tree to identify and fix the cause of a SERVFAIL after enabling DNSSEC

CaptainDNS · February 25, 2026

SERVFAIL after enabling DNSSEC: diagnosis and fix

A SERVFAIL after enabling DNSSEC points to a broken chain of trust. This guide covers the five causes, three diagnostic commands, and exact fixes for each scenario.

Diagram showing the DANE flow between an SMTP sender and Exchange Online with DNSSEC and TLSA

CaptainDNS · February 24, 2026

Deploy DANE for Exchange Online and Microsoft 365

Microsoft 365 has supported inbound DANE since 2024. This guide explains how to enable it, configure DNSSEC on your domain, and verify the deployment.