I am using a guide tecmint.com/setup-postfix . . .

1. Create host name. ie. a subdomain of the domain to be used in the root i.e.
   /var/www/rogerloveuk
   $ sudo hostnamectl set-hostname mail.rogerlovejoy.uk ✓

2. Create MX record on DNS for domain
   MX record @ mail.tecmint.com
   mail.tecmint.com [ip -address]

   First I created an A Record for mail.rogerlovejoy.uk then pointed the MX Record to that ✓

   Updated Aug 20th
   I have found advice to set a PTR (Pointer) record to enable a more acceptable route for other email servers recognise this one. This is effect a reverse lookup which when dealing with an ip address(no) ###.###.###.### will be directed to a specific domain, in this instance [rogerlovejoy.uk]

   This is acheived via the provider of the static ip address, Zen.

3. The next instructions are for the CLI

   $ sudo apt-get update -y
   $ sudo apt-get upgrade -y
   $ sudo apt install apache2 apache2-utils mariadb-server mariadb-client php7.4 libapache2-mod-php7.4 php7.4-mysql php-net-ldap2 php-net-ldap3 php-imagick php7.4-common php7.4-gd php7.4-imap php7.4-json php7.4-curl php7.4-zip php7.4-xml php7.4-mbstring php7.4-bz2 php7.4-intl php7.4-gmp php-net-smtp php-mail-mime php-net-idna2 mailutils

   So I will try
   
   $ sudo apt-get update
   $ sudo apt-get upgrade
   $ sudo apt install apache2-utils mariadb-server mariadb-client libapache2-mod-php7.3 php7.3-mysql php-net-ldap2 php-net-ldap3 php-imagick php7.3-common php7.3-gd php7.3-imap php7.3-json php7.3-xml php7.3-intl php7.3-gmp php-net-smtp php-mail-mime php-net-idna2 mailutils ✓

   When trying first command I received a response form an earlier command:
   unable to resolve host mail.rogerlovejoy.uk: Name or service not known

4. Installing Postfix Mail Server
   $ sudo apt-get install postfix ✓
5. This brings up a CLI 'Postfix Configuration' page see Postfix Config