The first thing you'll need to do is create a server.
If you have an existing server with Ubuntu 18.04, you can use ServerWand to connect to it.
Adding a server
From the Create menu click -> Server.
You can then choose whether to create a new server with Linode, DigitalOcean or connect to an existing server.
Linode and DigitalOcean are both world-leading VPS providers and are the easiest way to get started. They also provide free DNS hosting which we'll come onto later.
When selecting either of these providers you will be prompted to connect to your Linode or DigitalOcean account.
Once connected you will be provided with server region and size options. Server size can later be upgraded with your respective provider, where you can also enable server backups if required.
Select the Mailserver option if the server will be used to host POP/IMAP accounts.
Then press Save and your server will be configured.