I'm trying to configure Postfix on Ubuntu 18.04LTS. It's working, in the basic sense, but not doing everything I want. I've read some of the config help and examples, but I'm still not clear on what to do.

For each Ubuntu server I manage, I'd like these to work:

user1@ubuntu:~$ mail -s "Test" user2 <message-body

user1@ubuntu:~$ mail -s "Test" user2@ubuntu <message-body

user1@ubuntu:~$ mail -s "Test" user2@ubuntu.mydomainname <message-body

user1@ubuntu:~$ mail -s "Test" user3@myotherdomainname <message-body

I hope that's clear. Or

mail -s "Test" jdoe

mail -s "Test" jdoe@server678

mail -s "Test" jdoe@server678.domain1.org

...which would all deliver email locally to this server (server678) and the last one would be for mail which is destined for any other user NOT on this server but in domain2 (domain1 and domain2 are both internal workplace domains), and which will have to go through a relay host to get anywhere:

mail -s "Test" santa394@domain2.org

I don't know if I've made myself clear. Ask questions and I'll try to clarify what I want.

Kevin