Sometimes users follow instructions from a different non Bitnami guide which can cause issues, so I wanted to be sure you followed these exact steps.
We have a Support Tool that will gather relevant information for us to analyze your configuration and logs. Could you please execute it on the machine where the stack is running:
sudo /opt/bitnami/bnsupport-tool --runSMTPTool 1
Please note that you need to paste the code ID that is shown at the end.