Dmarc
_dmarc subdomain, TXT reject all, lose policy reject all, strict spf and DKIM policy
We offer no support for email whatsoever including settings, delivery/spam and so on.Usefull tools: https://mxtoolbox.com/ https://www.mail-tester.com/ https://isnotspam.com/ https://spamscorechecker.com/ https://www.port25.com/support/authentication-center/email-verification/ See DNS How to sent mail to mail-tester via WordPress Example given that your test mail address is "test-thisissomerandom@srv1.mail-tester.com" and your site is "site.com".