DomainKeys Identified Mail (DKIM) is a standard that allows senders to sign their email messages with a cryptographic key. Email providers then use these signatures to verify that the messages weren't modified by a third party while in transit.
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An email message that is sent using DKIM includes a DKIM-Signature header field that contains a cryptographically signed representation of the message. A provider that receives the message can use a public key, which is published in the sender's DNS record, to decode the signature. Email providers then use this information to determine whether messages are authentic.
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Different domain name providers have different procedures for updating DNS records. The following list links to the documentation for several common providers. This list isn't exhaustive and inclusion in this list isn't an endorsement or recommendation of any company's products or services.
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​GoDaddy - Add a CNAME record
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​DreamHost - How do I add custom DNS records?
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​Cloudflare - How do I add a CNAME record?
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​HostGator - Manage DNS Records with HostGator/eNom
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​Namecheap - How do I add TXT/SPF/DKIM/DMARC records for my domain?
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​Names.co.uk - Changing your domains DNS Settings
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​Wix - Adding or Updating CNAME Records in Your Wix Account
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​123 reg - How do I set up a CNAME record on my domain name?
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​Blue Host - How To Setup a DNS SPF
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