SMTP

SMTP transport, STARTTLS, MTA-STS, and TLS reporting.

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Related topics

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.
Deliverability
Why legitimate email ends up in spam, and how to keep it out of it.
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