DKIM: DomainKeys Identified Mail for Email Integrity
DomainKeys Identified Mail (DKIM) is an email authentication method where your sending server adds a cryptographic signature to each message, and receivers verify it using a public key published in DNS.
DKIM proves the message content was not changed in transit and links the message to your domain. It improves deliverability and is a core input for DMARC. Most providers generate DKIM keys for you, you publish them as DNS records, then enable signing in the provider.
Example
A DKIM public key is published under a selector, for example:
selector1._domainkey.example.com TXT \"v=DKIM1; k=rsa; p=MIIBIjANBgkq...\"Frequently Asked Questions
A selector is a label that lets you publish multiple DKIM keys for the same domain. It appears in the DKIM-Signature header and points to the correct DNS record.
Yes, via different selectors. This is normal when you use multiple sending platforms or when you rotate keys.
Rotate on a schedule that matches your risk tolerance and provider capabilities. Many teams rotate every 6 to 12 months, or when access changes.
Common causes are wrong selector, DNS propagation not finished, record split incorrectly, extra spaces or quotes, key length limits in DNS UI, or the provider not actually signing outgoing mail.
It helps, but you need DMARC to tell receivers what to do with failures and to enforce alignment with your visible From domain.
Both can work. RSA is widely supported. Ed25519 can be faster and smaller, but support varies by provider and receiver. Use what your email platform supports reliably.
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