"By default Ultimate Email Validator checks your system for your primary DNS server. As a benefit, you can specify custom DNS Servers in the DnsServers property of the EmailValidator class. Ultimate Email Validator will attempt to connect to each one, until a successful connection is made, and then use the first responsive DNS Server for the remainder of the Email Validator session."
The text above states that it is possible to specify custom DNS servers to validate against. But the mentioned property is readonly.
Product version: Ultimate Studio Package 6.8.4155 Standard