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RFC · EmailStandard explained

RFC 5321: SMTP: Transferring email between servers

Summary

RFC 5321 describes SMTP for relaying, delivery, queueing and error handling between mail servers. Email is a federated queueing system rather than a direct end-to-end connection. Deliverability combines protocol compliance with reputation and abuse protection.

Ideas

  • MX records determine the responsible destination servers.
  • Reply codes distinguish temporary from permanent errors.
  • Store-and-forward bridges temporary unreachability.

Facts

  • RFC 5321 replaces RFC 2821.

Remarks

  • RFC 5321 has the status “Draft Standard”; current errata and successor documents should also be checked.

Recommendations

  • Monitor queue, bounces, DNS and TLS together.
  • Configure SPF, DKIM and DMARC on top of the SMTP basics.

References

Read the RFC at the RFC Editor

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