Knowledge Base

Practical, technical guides for SPF, DKIM, DMARC, DNS, and email deliverability — written to help you fix issues, not just read about them.

Browse by topic

Email Authentication
How SPF, DKIM, and DMARC work together to prove an email really came from your domain.
SPF
Sender Policy Framework: syntax, DNS lookup limits, permerror, and common misconfigurations.
DKIM
DomainKeys Identified Mail: selectors, signing, alignment, and key rotation.
DMARC
DMARC policies, alignment, and aggregate/forensic reporting.
DNS
The DNS record types and concepts email authentication and delivery depend on.
SMTP
SMTP transport, STARTTLS, MTA-STS, and TLS reporting.
Deliverability
Why legitimate email ends up in spam, and how to keep it out of it.
Gmail
Gmail and Google Workspace sender requirements and troubleshooting.
Microsoft 365
Microsoft 365 / Outlook sender requirements and troubleshooting.
Providers
Per-provider setup guides for SPF, DKIM, and DMARC across common email and marketing platforms.
Free Tools
How to use MXFend's free checkers and what their results mean.

Featured articles

SPF PermError explained
SPF PermError means the SPF record is invalid and cannot be evaluated correctly by receiving mail …
SPF Permerror: Too Many DNS Lookups
SPF permerror usually happens when your SPF record exceeds the maximum DNS lookup limit. Once the …
What is DKIM?
DKIM adds a cryptographic signature to outgoing emails, allowing receiving servers to verify that the message …
What is DMARC?
DMARC lets you tell receiving mail servers what to do with email that fails SPF or …
What is SPF?
SPF helps receiving mail servers verify which systems are allowed to send email for your domain.
Why are my emails going to spam?
Spam placement is usually caused by a combination of technical authentication failures, poor sender reputation, blacklist …
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