Some notes on where email security DNS records are kept.

dig example.org TXT #SPF
dig _dmarc.example.org TXT #DMARC
dig {SELECTOR}._domainkey.example.org TXT #DKIM

Where does the DKIM {SELECTOR} come from? It's vendor specific; for GMail it's google, for Mailgun it's k1, etc. There are a few lists of selectors on the internet:

• https://github.com/zkemail/registry.prove.email/files/14850741/selector_frequencies.txt
• https://topdeliverability.com/email-service-providers-handbook/
• https://github.com/ryancdotorg/dkimscan/blob/master/dkimscan.pl