possible? yes. The better question you should ask yourself would be "does the use case make sense?"
Linux containers are ephemeral, which means that you will lose all data from your email server on a container restart. If you're just setting up a postfix SMTP server in a container, and forwarding the guest's port 25 to the host, I don't see why not. You probaby won't have any app scaling support or the likes, though. I could be wrong about that. I've never attempted to set up a clustered SMTP server configuration before.