SPF

Sender Policy Framework records, include mechanisms, and lookup limits.

8 articles

March 2026

Diagram of the 6 causes of an SPF PermError with a diagnostic tree and error indicators

CaptainDNS · March 4, 2026

SPF PermError: the complete guide to understanding, diagnosing and fixing this error

Diagnose and fix SPF PermError: the 6 causes, the impact on DMARC and the methods to repair your SPF record.

SPF Flattening vs SPF Macros comparison with workflow diagrams and decision matrix

CaptainDNS · March 3, 2026

SPF Flattening vs SPF Macros: Which Approach Should You Choose to Stay Within the 10 Lookup Limit?

Detailed comparison of SPF flattening and SPF macros: how they work, advantages, disadvantages, and a decision matrix to help you choose the right approach.

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.

January 2026

Postmark Dashboard with Message Streams and DKIM DNS configuration

CaptainDNS · January 28, 2026

Postmark (ActiveCampaign): Complete Technical Guide to Transactional Email

Detailed technical guide for developers: DNS configuration (DKIM, custom Return-Path), REST API vs SMTP, Message Streams, dedicated IP, webhooks and 2026 pricing.

Mailgun dashboard with Domain Authentication and REST API configuration

CaptainDNS · January 21, 2026

Mailgun: Complete Technical Guide for Transactional Email

A detailed technical guide for developers: DNS configuration (SPF, 2048-bit DKIM with autorotation), REST API vs SMTP, dedicated vs shared IP, limits and webhooks.

SendGrid dashboard with Domain Authentication and Web API v3 configuration

CaptainDNS · January 19, 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

Illustration of the 3 CaptainDNS MCP widgets in ChatGPT

CaptainDNS · December 17, 2025

Connect CaptainDNS to ChatGPT via MCP: 3 widgets for DNS audits and deliverability

Add the CaptainDNS MCP server to ChatGPT and use 3 widgets to troubleshoot DMARC/DNS and analyze email headers without leaving the conversation.

October 2025

What Is ARC (Authenticated Received Chain)?

CaptainDNS · October 23, 2025

ARC: keeping trust in an email as it crosses intermediaries

ARC (Authenticated Received Chain) lets every relay forward, sign, and seal the authentication results it observed so the final server can decide whether to trust the message.