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.