# What is DKIM? Definition and examples · Leadraft

URL: https://leadraft.co/glossary/dkim
Summary: DKIM (DomainKeys Identified Mail) is a cryptographic signature added to email so receivers can verify which domain sent it and that it wasn't altered.

Glossary · Email & deliverability · Last updated October 31, 2026

# DKIM

DKIM (DomainKeys Identified Mail) is a cryptographic signature added to email so receivers can verify which domain sent it and that it wasn't altered.

**Also called:** DomainKeys Identified Mail.

DKIM is defined in RFC 6376. The sending server signs selected headers and the body with a private key and adds a `DKIM-Signature` header. The receiver fetches the matching public key from DNS, at `selector._domainkey.yourdomain.com`, and checks the signature.

A passing DKIM signature proves the message was signed by the domain in its `d=` tag and that the signed parts weren't changed in transit. Unlike SPF, it survives forwarding, which makes it the more reliable of the two for DMARC alignment.

Google requires bulk senders to Gmail to set up DKIM as well as SPF, Yahoo requires both for bulk senders, and Outlook.com requires high-volume senders to pass DKIM. Most mailbox providers and sending tools give you the DNS record to publish; the step people skip is making sure the signing domain matches the From domain.

For cold email, enable DKIM on every sending domain and mailbox before warm-up, and check a real message's headers for `dkim=pass` with your own domain rather than the provider's default.

## Example

A received message shows `dkim=pass header.d=getacmeagency.com`. The signature matches the From domain, so it can satisfy DMARC alignment.

## Sources

1.  1.[IETF, RFC 6376: DomainKeys Identified Mail (DKIM) Signatures](https://www.rfc-editor.org/rfc/rfc6376)
2.  2.[Google, Email sender guidelines](https://support.google.com/a/answer/81126)
3.  3.[Yahoo, Sender best practices](https://senders.yahooinc.com/best-practices/)
4.  4.[Microsoft, Outlook.com Postmaster policies](https://substrate.office.com/ip-domain-management-snds/postmaster/Policies)

## Related terms

-   [SPFSPF (Sender Policy Framework) is a DNS record that lists which servers are allowed to send email for a domain, so receivers can spot forgeries.](https://leadraft.co/glossary/spf)
-   [DMARCDMARC is a DNS policy that tells receivers what to do with mail that fails SPF and DKIM alignment for your domain, and where to send reports.](https://leadraft.co/glossary/dmarc)
-   [Email deliverabilityEmail deliverability is the ability of your emails to reach recipients' inboxes rather than bouncing or landing in spam.](https://leadraft.co/glossary/email-deliverability)
-   [Email warm-upEmail warm-up is gradually increasing the volume sent from a new domain or mailbox so mailbox providers learn to trust it before full campaigns.](https://leadraft.co/glossary/email-warm-up)

## Further reading

-   [Cold-email checklist for agencies](https://leadraft.co/blog/cold-email-checklist-for-agencies)

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Last built: 2026-11-09