Mail server configuration help

We are looking for someone to help us configure a mail server on Ubuntu 20.04 LTS. The mail server is currently working, but needs some more configuring and documentation. We are looking for someone to prepare: 1) instructions on how to another domain to the mail server to allow the mail for another domains to be received by the mail server; 2) instructions on how to configure Cloudflare for the new domain(s); There is no web mail on the mail server. The mail server stores the mail until a Windows client downloads it from the mail server. Therefore there is very little configuring to do. You must have experience managing a mail server. This is a very simple job for someone who has already manages a mail server.