Moving on to the next topic: DNS.
I'm not really a DNS expert, but as I see it there are 2 basic options:
Manage DNS locally on the server. Advantage: ease of use (Virtualmin) and full control. Disadvantage: if the VPS goes down (with DNS) then mail service is unnecessarily interrupted.
Use external DNS service, either provided by domain registrars, or seperate DNS provider (free/paid). Advantage: redundancy (assuming a good provider) ensures that even when the VPS is down, mail and other Google Apps services are unaffected. Disadvantage: not managed by Virtualmin, sometimes not very flxible.
Of course there are combinations and variations:
Master DNS on the VPS and external Secondary (backup) DNS, or vice versa. This is usually only possible with paid DNS services, as most registrars and free DNS services do not support master <-> secondary configurations (but there are exceptions, eg. http://xname.org).
Use another (cheap) VPS as DNS backup. This has the advantage of centralized management by Virtualmin (or Webmin?).
Use two external DNS services, set up as Master <-> Secondary.
For few domains, manually updating two DNS systems isn't too hard. Those may be local and external or both external.
So, if mail and maybe other services are offloaded to Google Apps, it's a good idea to have an external DNS service. But should we keep the local DNS as well? I think that the answer depends on two factors:
How good is the external DNS? If the provider runs several servers on different networks around the world, then local DNS isn't really needed. Unless...
... web sites and scripts generate a lot of outbound traffic (eg. sending newsletters). In this case the local DNS server may improve the performace of such operations, enough to justify the RAM it uses. Alternatively, if the VPS host runs a DNS server on the same LAN, then it may obviate the need for a private (VPS local) DNS.
In case there is no need for a local DNS, the steps to disable it are:
For every existing server and sub-server - Uncheck the following: Edit Virtual Server -> Enabled Features -> DNS domain enabled.
Uncheck the following: Virtualmin -> System Settings -> Features and Plugins ->
BIND DNS domain
Slave DNS domain
Select (check) and click Disable Now and On Boot the following: Webmin -> System -> Bootup and Shutdown -> bind9
Comments, corrections and additions please...