Piki wrote:
I didn't say shop.example.com was mandatory, I was using the example from the tutorial. It did seem to require that my mail server be hosted on mail.example.com.
A subdomain is just an "alias" for a server. You can redirect it to whatever IP you want. If you have a website called example.com which is in IP 1.1.1.1 but your mailserver is at 2.2.2.2, you can redirect example.com to 1.1.1.1 and mail.example.com to 2.2.2.2. Of course, calling the subdomain mail.* is not mandatory, but the most common way of configuring your email server.