Inconsistent Test Email Results

I’m trying to get Postman SMTP to work, but can’t get test emails delivered to external servers. It delivers to other domains on my hosting account fine, but not to gmail or centurylink accounts. In every instance, the session transcript shows no errors. If I use my email client, I can send messages from the same email to the centurylink and gmail accounts without a problem.

I’m stuck. Can anyone help?