Send an email to check-auth@verifier.port25.com
You will get an email back that looks like this:
This message is an automatic response from Port25's authentication verifier service at verifier.port25.com. The service allows email senders to perform a simple check of various sender authentication mechanisms. It is provided free of charge, in the hope that it is useful to the email community. While it is not officially supported, we welcome any feedback you may have at <verifier-feedback@port25.com>. Thank you for using the verifier, The Port25 Solutions, Inc. team ========================================================== Summary of Results ========================================================== SPF check: pass "iprev" check: pass DKIM check: pass SpamAssassin check: ham ========================================================== Details: ========================================================== HELO hostname: mail-vs1-xe34.google.com Source IP: 2607:f8b0:4864:20::e34 mail-from: test@testing.com ---------------------------------------------------------- SPF check details: ---------------------------------------------------------- Result: pass ID(s) verified: smtp.mailfrom=test@testing.com
These results should help you diagnose your sending issues, if you need help please forward the entire message to our support team.