Workspace DKIM configured but no DKIM-Signature
I'm trying to configure my legacy G Suite GMail to use DKIM authentication for my custom domain.
Currently no DKIM-Signature header is being added to outbound emails, and therefore the authentication result is dkim=none. Confirmed with manual header inspection, and dmarctester.com. Have also noticed there is a X-Google-Dkim-Signature in the headers, but that looks like an additional thing, rather than replacing the standard DKIM mechanism?
There's a valid SPF record, and the DMARC policy is currently none, so email is still being delivered, but I still want DKIM to be active.
In the Workspace admin settings -> Authenticate Email, it currently says "Status: Authenticating email with DKIM.". There's a corresponding DNS text record google._domainkey.<mydomain>.com using the details from that admin page. A lookup of the DNS record with mxtoolbox shows that it's a character for character match, and is a valid DKIM record.
I've tried removing the DNS record completely, generating a new DKIM key in the Workspace admin page, re-adding the DNS record, and starting authentication again. There's greyed out Cancel & Save buttons at the bottom of that Admin Authentication Email page, but I'm guessing that's normal?
Any other things I can try to get Workspace to use DKIM?