After installing and configuring `Postfix 3` on my `CentOS 8`, I'm still a bit confused about the role of `smtp`, `smtps` and `submission` services configured in `master.conf` file. 

All of them appear to be an instance of the same type application, but with different configurations (at least that's what I understand is the recommendation). 

Can anybody explain on short what are the meanings of each of these services? 

N.B. Would be great to provide documentation reference too.

Searching on the internet I can see that responses vary a bit on this topic, so I would be grateful if a blueprint would be set out. If examples can be provided that's also very welcome.