As always Troy has put loads of effort into writing a really high quality blog post that shares some really useful information for devs working on this stack (and for non .Net devs too).
this is serving up some static content, and a string lookup in a hash table.
a single cheap vps with 768mb of ram should be able to handle thousands of requests/second without issue.
(50 chars email average + 2 * 4 byte pointers) * 10M entries => 512mb ram
(and with some noddy splitting by email domain you could probably quarter that)