Email authentication, deliverability and DNS guides that get to the point.
A static knowledge base for SPF, DKIM, DMARC, inbox placement, PTR records, Microsoft 365, Gmail issues, warm-up, complaints and all the usual reasons email goes wrong.
Core guides
Start here if you want the big building blocks, then move into provider-specific and problem-specific pages.
SPF setup guide
What SPF does, how it is evaluated, common syntax, includes and lookup limits.
DKIM explained
Selectors, keys, DNS records, alignment and troubleshooting failed signatures.
DMARC guide
Policies, alignment, aggregate reports and staged movement toward enforcement.
Email deliverability basics
Authentication is only part of the picture. Reputation, content and list quality matter too.
DNS basics for email
MX, A, PTR, SPF, DKIM, DMARC and related records in plain English.
General troubleshooting
A practical sequence for finding out why mail fails, gets delayed or lands in spam.
Problem Specific
SPF too many lookups
Why SPF breaks with includes and flattening options that avoid permerror.
SPF flattening
When to flatten, risks to watch, and when simplification is better than automation.
Why Gmail puts mail in spam
The most common Gmail-specific causes and what to check first.
PTR records for email
Reverse DNS, HELO, forward-confirmed reverse DNS and trust signals.
Email warm-up guide
How to ramp volume more safely and why warm-up alone does not create good reputation.
How to read DMARC reports
Understand aggregate XML reports and what to do with the data.
Platform and provider guides
Enable DKIM and understand the extra DNS records involved.
Mailgun SPF and DKIMAuthentication basics for Mailgun sending domains.
Gmail bulk sender basicsAuthentication and hygiene requirements for higher-volume senders.
Subdomain vs root domainWhy many senders isolate reputation on a sending subdomain.