1. A method in a proxy server for responding to resource unavailable errors, comprising: receiving, from a client device, a request for a network resource hosted at an origin server for a domain, wherein the request is received at the proxy server as a result of a DNS (Domain Name System) request for the domain resolving to the proxy server, and wherein the origin server is one of a plurality of origin servers that belong to different domains that resolve to the proxy server and are owned by different entities; requesting the network resource from the origin server; receiving a response from the origin server that indicates that the network resource is unavailable; and transmitting a custom error page to the client device that indicates that the requested resource is unavailable.