They are also an American organization with servers in America. Same with Yahoo. If you really need a clearnet email provider, go with something hosted in Russia. Their government and intel agencies are much less likely to cooperate with Western LE. Yandex (mail.yandex.com) and Rambler (mail.rambler.ru) are good examples. Rambler's interface is in Russian, there is no English option, so you'll have to paste stuff into a translation service to figure out what you're doing, and both require JavaScript to use the webmail interface, but you should only need to use the web interface long enough to configure your desktop email client (Thunderbird + Enigmail + Torbirdy) to connect over Tor. Obviously you should PGP encrypt all messages, so the point of hosting in Russia is to make access to your metadata more difficult.