Question: how to configure mail server in linux ubuntu step by step?
Answer: Log In and Update Your Server. Log into your server using SSH. ... 
Install Bind. To configure a DNS server that will use Postfix we'll need an additional tool – Bind. ... 
Configure /var/cache/db. test. ... 
Add New Zone to Bind Configuration. ... 
Configure /etc/bind/named. ... 
Restart Bind.