Received Virtualmin error that 127.0.0.1 isn't listed in /etc/resolv.conf

This is typically because your IP address is being dynamically assigned by DHCP. While obtaining an IP address, the DNS servers provided by your DHCP server are used in place of what's currently setup on your server.

For a server, we'd suggest using static IP's where possible.

Can I run each service on a different machine?

Yes for some services, no for others.

It is possible to use LDAP for mail user configuration, though this is not a comprehensive solution. Many of the features of Virtualmin can be re-implemented manually on the mail server, using Webmin and Usermin, but per-domain spam/AV configuration is not possible in this setup. The other option is to use Virtualmins ability to run commands before or after creation/update/delete of user accounts. One could write a custom command that makes use of ssh to perform actions on a remote mail server.

Domain Name Service

Automatic DNS Slave Configuration - Configuration of automatic DNS slave creation and management.

DNS FAQ - Frequently asked questions about DNS.

Domain Name Server Troubleshooting - Troubleshooting common problems with domain name service.

Domain Registration With Virtualmin - Use of the Virtualmin Registrar plugin, which allows users and administrators to register domains from within Virtualmin using one of several DNS reg