They are ns1.mrdomain.com, ns2.mrdomain.com, ns3.mrdomain.com and ns4.mrdomain.com, depending on the server on which your hosting is configured.
Using MrDomain's DNS servers
Note that to be able to assign our DNS servers you'll need to have a hosting or redirection and parking service associated to your domain, in other case you won't be able to use them.
Use MrDomain's DNS servers for domains in other Registrar You won't be able to use our DNS if the domain isn't registered with us.
Remember that the DNS modifications can take up to 6-12 hours to propagate thru the Network, till then the domain will still point to the previous DNS servers.