DKIM (DomainKeys Identified Mail) is an email authentication and security protocol that allows parts of sent emails to be signed so that receivers can verify the validity of the sender domain.

DKIM is a TXT record added to the domain's DNS under the "provider"._domainkey name. IN TXT "v=DKIM1; k=rsa; p=MIIBIjAN…"

The content of the record is a value generated by the email provider.

For Google Workspace, go to "Apps", "Google Workspace", "Gmail", Authenticate Email (DKIM) to enable and retrieve the value to enter in the DNS record.

Then add a DNS record of type TXT for the name google._domainkey and the value from Google, which starts with v=DKIM1; k=rsa; p=….

To check the DKIM record, use host or dig:

$ host -t TXT descriptive text "v=DKIM1; k=rsa; p=MIIBIjAN…
$ dig +short -t TXT