Server gets emails but all letters going to nowhere

Could you help to understand:

  1. Hestia installed without spam assasin
  2. Was pointed default value hosting.domain.gld
    After i try to fill one of domains wich was hosted
  3. Added domains and users
  4. Added ssl and etc.
  5. After i noticed that all post to emails under domaing reached server
  6. All letters which send from domains( pop3, web, imap) just disappaering
  7. Even dosen’t receive them
    How i can check this moment?

and + question
Is it need to fill in hostname a domain which must be parked on server ?
for example, we can use
and in RSD yse same
Or i must use only a real domain wich are on server, has dkim and etc.