you mentionned fake name ... but. one mail server can host several domains. (this is what ispconfig mail server is done for) hostaname -f , for me, has nothing to do with postfix config ... and so on with all other mx record domain that can point to the mail server. eg mail server name : mail1.domain.local (hostname -f) BuT mx record for domain.com => mail1.domain.com hosted by mail1.domain.local mx record for domain2.eu=> mail1.domain2.eu hosted by mail1.domain.local etc etc . so this is very strange why you use the term , fake name , for every other mail domain hosted by mail server first one is always a "fake name" . domain.com is a fake name for domain2.eu for example ?