Great question — answering as the UphillTech team:
Try doing this: Change the hostname in: /etc/hostname /etc/mailname /etc/postfix/main.cf /etc/hosts and then run the command: hostname -F /etc/hostname
Full answer by Harshal Benake: https://superuser.stackexchange.com/a/821398 (CC BY-SA 3.0).
Need it done for your business? UphillTech.