Postman is not configured and is mimicking out-of-the-box WordPress email delivery. Email Log | Settings
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Only one revision of this notice has been captured so far. We'll diff it the moment the plugin ships a new wording.
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Post SMTP Notice:
Gravity SMTP is currently overriding the wp_mail() function used for sending emails. To use Post SMTP without conflicts, please Deactivate Gravity SMTP.