DKIM & SPF Definition
DKIM & SPF keys are an Email Authentication method used between servers to approve the Sender’s Identity and prevent phishing & spam.
When server1.com sends an email from server1.com to server2.com, server2 will check if server1.com keys match based on DNS records, registered as TXT entries:
- For SPF, on server1.com
- For DKIM, on selector._domainkey.server1.com
To debug the keys configuration, use an online tool such as https://www.mail-tester.com/spf-dkim-check or from the console:
$ dig server1.com txt
$ dig selector._domainkey.server1.com