Backup MX setup
To use mailcow as a backup MX, you need a primary MX with a priority lower than your backup MX (e.g. primary MX: 10, backup MX: 20).
Install mailcow using "mx01" as hostname on server 1.
Install mailcow using "mx02" as hostname on server 2.
Create the necessary DNS records in your domain. Give "mx01" a priority of "10", "mx02" a priority of "20".
Create your domain "example.org" on both servers.
On server 2 - "mx02" - check "Backup MX" when creating your domain. Leave it unchecked on server 1.
You will need to create mailboxes (and all aliases) on both servers. Though mailboxes and aliases on server 2 will not be used, they must exist to allow relaying a users mail. This behaviour will be fixed/optimized in future versions of mailcow.
