It is important to choose a hostname that you will not be using for any account.
Do not choose a potential service subdomain as a hostname (for example, cpanel.example.com or whm.example.com).
You should choose something that will be socially acceptable, as it will appear in all mail headers.
Choose a hostname that is 60 characters or fewer.
Your hostname must be a
FQDN.
In English, a hostname should consist of a name and a domain name.
All valid hostnames should have 2 dots in them.
Hostnames should never begin with “www”.
Hostnames should also not begin with a digit, nor end with a hyphen (“-”).
Only use lowercase, Latin-script letters in hostnames.