Bitnami packages and configures already existing applications. We can only offer support and help on basic and most frequent application configurations. Always based on the default configuration or on our guides. We have a section in our documentation that explains how to configure the SMTP settings in the application
But we do not control how the application sends the messages. If the question is related to the application itself, probably someone with more experience and knowledge about the application can help you better than we can.
We suggest you to post your question on the official support forums of the application so others can help you with your issue.