DNS - TXT record

txt records are DNS record where any text value can be stored.

They are used for multiple purpose such as:

• email authentication with
  • SPF to list the server that sends email
  • DKIM where the public key is stored to decrypt the email signature
  • DMARC where the actions that should be taken on bad email are set.
• but also for domain ownership verification for instance:
  • for certificate issuance
  • to become the postmaster on Search Console / Email such as https://postmaster.google.com/

For instance, if we want to known:

• the TXT record of google.com
• on the nameserver ns2.google.com

you would DNS query the database record with nslookup and the following command:

nslookup -type=TXT google.com ns2.google.com