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.