You can have one server that supplies all Internet services (such as mail or web). These services can run on one computer with a single IP address.
You can have multiple host names in the same zone for a single server. For example, you might want to have the domain name www.example.com resolve to the same IP address as ftp.example.com or mail.example.com. This domain appears to be several servers to anyone accessing the services, but they’re all one server at one IP address.
Setting up DNS records for this service is easy: add aliases to the machine DNS record. Setting up DNS names for these services doesn’t enable or configure the services. It provides names that are easy to remember for each service offered. This can simplify setup and configuration of the client software for each service.
For example, for every service you want to show, do the following:
Create mail.example.com to enter for mail clients.
Be sure to select the “Create an MX record for this host name” for the DNS host name you create in the DNS pane of the Server app.
Create www.example.com to enter on web browsers.
Create afp.example.com for Apple File Sharing in the Finder.
Create ftp.example.com to enter on FTP clients.
As your needs grow, you can add computers to the network to handle these services. Then, remove the alias from the machine’s DNS record and create a record for the new machine, and your client’s settings can remain the same.