As first troubleshooting tip, please check what Amasty SMTP Debug Log and Amasty SMTP Sent Email Logs say.
Please enable the logs in the main module configuration page.
Where сan I see these logs in Magento 1?
- Please go to System > Tools and enable Smtp Emails Debug Log.
- Please go to System > Tools and enable Smtp Emails Sent Log.
Where сan I see these logs in Magento 2?
- Please go to Reports > SMTP and enable SMTP Debug Log.
- Please go to Reports > SMTP and enable SMTP Emails Sent Log.