I edited your post. Please, next time format your post according to the following guide: How to format your forum posts
In short: please, use </> button to share codes, terminal outputs, error messages or anything that can contain special characters which would be interpreted by the MarkDown filter. Use the preview feature to make sure your text is formatted as you would expect it and check your post after you have sent it so you can still fix it.
Regarding your issue, the original problem was postfix not starting in a container which ws answered by @bluepuma77. How AWX work I think is a different issue and I’m not even sure that this is the best forum to ask about that just because it is running in a container. AWX 17.1.0 is a pretty old version by the way. Is that still supported? I guess you stil use it because latest versions require Kubernetes if I remember correctly.
Generally you would need log messages to see why certain features don’t work. I checked your compose file and all I can see is a variabale that I can’t find in the documentation of AWX and not even in the sourcecode: POSTFIX_ENABLED.
Please, explain why you think it is Docker-related (besides what we already discussed about postfix and systemd) so we can focus on your real issue to help you.
You can also find some links about the Ansible community to find forums where you can ask about Ansible or AWX