DKIM records are published at a selector-specific subdomain: selector._domainkey.yourdomain.com. DomainScan probes common selectors (google, default, mail, s1, s2, k1) automatically. If your selector name is non-standard, enter it manually in the selector field. Also check that your email provider has finished setting up signing — some providers take up to 48 hours to activate DKIM after you publish the key.
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