---
title: "SPF, DKIM and DMARC"
description: "SPF, DKIM and DMARC are the three DNS-based email authentication standards. SPF lists which servers may send for a domain, DKIM signs messages cryptographically, and DMARC tells receivers what to do when mail fails them and sends reports back."
canonical: "https://omnichannels.ai/glossary/spf-dkim-dmarc/"
language: "en"
updated: "2026-10-10"
publisher: "BroadNet Technologies"
brand: "OmniChannels.ai"
---

# SPF, DKIM and DMARC

Canonical: https://omnichannels.ai/glossary/spf-dkim-dmarc/
Language: en
Publisher: OmniChannels.ai by BroadNet Technologies

**Definition:** SPF, DKIM and DMARC are the three DNS-based email authentication standards. SPF lists which servers may send for a domain, DKIM signs messages cryptographically, and DMARC tells receivers what to do when mail fails them and sends reports back.

SPF (Sender Policy Framework, RFC 7208) is a DNS TXT record listing the IP addresses and services allowed to send mail using the domain in the envelope sender. Receivers check the connecting server against it. SPF allows at most 10 DNS lookups, a limit often exceeded when many vendors are added.

DKIM (DomainKeys Identified Mail, RFC 6376) adds a digital signature to each message's headers. The receiver verifies it with a public key published in DNS under a selector. Gmail requires keys of at least 1,024 bits and recommends 2,048.

DMARC builds on both. A domain publishes a policy (p=none, quarantine or reject) and reporting addresses. A message passes DMARC when SPF or DKIM passes for a domain aligned with the visible From domain. DMARC was originally RFC 7489, which was replaced in May 2026 by a new standards-track specification, RFC 9989.

Gmail requires SPF, DKIM and DMARC for bulk senders. Roll out DMARC by starting at p=none, reading the reports to find every legitimate sender (CRM, help desk, messaging platform), fixing their SPF and DKIM, then moving to quarantine and reject.

## Example

```
_dmarc.example.com TXT "v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com"
```

## Sources

- [RFC 7208: Sender Policy Framework (SPF)](https://www.rfc-editor.org/rfc/rfc7208)
- [RFC 9989: Domain-Based Message Authentication, Reporting, and Conformance (DMARC)](https://www.rfc-editor.org/rfc/rfc9989)