I have a list of approximately 13K free email/webmail providers from circa 2000. Obviously the vast majority of these services have gone out of business, and the domains have either lapsed, or been snatched up by cybersquatters, who have put up a "for sale" sign and little else.
I'd like to prune the list down to free email/webmail providers that still work. Obviously, checking each entry manually is not feasible. What would be some automated ways of pruning the list down to candidate entries?