[ubuntu-za] Postfix explained

[Charl Wentzel]

Hi Guys

Every now and then I have an application that requires Postfix to be 
installed.  I assume this is because it wants to send email 
notifications.  I always get stuck at the point where you need to choose:
1. None
2. Internet Site
3. Internet with Smarthost
4. Satellite system
5. Local only

Try as I may, I have never found a simple site/document that explains 
the basic differences between these items and when to use each of them.  
The site I found simply tell you how to setup a specific option for a 
specific application without really explaining why.  So I just drop it 
and always select "none", just to get it out of the way.

I think its time I get to know these items. Any one know of a good doc 
site that give a nice overview and explains these selections.  I would 
like a nice overview and some examples.  If you know of something, 
please let me know.

My current application is a GitLab installation as a VM on a hosted 
server.  The VM is behind a NAT firewall and I connect to it via 
OpenVPN.  I have my email setup on Hetzner on my own domain.

Thanks
Charl