I was able to make it work following this guide:
It is my configuration:
authentication: plain # plain, login, or cram_md5
default_name: Instructure Canvas
It is important that you have to restart the services after that:
sudo /opt/bitnami/ctlscript.sh restart
Our bnsupport does not gather the content of your
outgoing_mail.yml. Please ensure you have the correct indentation.
Could you try it with a GMAIlL or a mailtrap account to check if the issue could be related to the SMTP provider?