Additional manually configured nameservers
If you are manually configuring other nameservers to be secondaries for
domains created using Virtualmin, you should add their hostnames to this text
box. This will ensure that the required NS records are added to the
DNS zone, and that the secondaries are used.
If you have configured Webmin to automatically create slave domains on
secondary nameservers, their hostnames do not need to be entered here. Instead,
Virtualmin will add them to the DNS zone automatically.