Notes
How to check DKIM and SPF records for your domain
- https://dkimcore.org/tools/keycheck.html
- https://dkimvalidator.com/
- https://www.mail-tester.com/
- https://www.sparkpost.com/email-tools/
or send an email to check-auth@verifier.port25.com
or send an email to check-auth@verifier.port25.com