Use an additional email testing tool, e.g. MailTester: https://www.mail-tester.com/ https://www.mail-tester.com/ There are others too, many have a free quota t

Use an additional email testing tool, e.g. MailTester: https://www.mail-tester.com/ https://www.mail-tester.com/ There are others too, many have a free quota that you can use a few times a day. With MailTester you can retest the same email after changing things as well. Perhaps Postmaster missed something.