FQDN virtualmin/webmin installation

Can someone make it absolutely clear the ideal way of installing the webmin/virtualmin and hostname to be used as I am a bit confused after some experience and some reading of this forum.

I’ve got a VDS/VPS with one provider, they require at least one domain name to be used. So lets say it is domain.com

Then, we download and install virtualmin script.
During installation we enter FQDN as domain.com

One of the web domain names on this server is also domain.com (same as hostname)
Then i read here that IT IS NOT A GOOD PRACTICE to have hostname and same domain name on the same server.
For some reason web domains on that server do not receive mail (Postfix) unless I change hostname in to host.domain.com. If server get rebooted hostname get changed back to domain.com and I have to go to Network Configutation and reset it back in to host.domain.com
Why is this happening?
The questions are -

  1. does VPS domain name shoud be domain.com?
  2. Virtualmin installation via install.sh script, should i give host (server) a name “domain.com” or just plain hostname word like “webserver” (without .tld)?
  3. Can I host a “domain.com” on that server right after and have no conflicts with the domain and hostname?


FQDN (fully qualified domain name) can be mydomain.tld or something.mydomain.com. So when you need to set for any reason your FQDN you dont need to use mydomain.com but instead you can use something.mydomain.com. Same can be applied for your hostname and only inportant thing is to be FQDN.