It's a magical kingdom..
So being a bit bored, I figured I'd read this lot's blog post about their AT&T 'blocking' episode. Which was.. quite the tirade regarding heinous crimes against 'net neutrality, and dastardly attacks against a small company trying to save the planet. That blog post referred to a reddit thread saying some users in Chicago were experiencing connectivity problems. But not all AT&T users, which seemed a little odd for the Death Star given they can usually destroy entire planets.
Tutanota also mentioned they were a cloud service, floating in a secure data service somewhere in Germany, and powered by the cleanest, greenest renewable electrons. Or photons. Not that they probably have much control over how the photons are powered, but that's digressing somewhat. But there are perhaps some more important issues-
inetnum: 81.3.6.160 - 81.3.6.175
netname: TUTAO-NET
descr: Tutao GmbH
route: 81.3.6.0/24
descr: as24679.net / SServ
origin: As24679
remarks: -- AS3320 Deutsche Telekom AG --
import: from AS3320 accept ANY
export: to AS3320 announce AS-SSERV
remarks: -- AS3356 CenturyLink --
import: from AS3356 accept ANY
export: to AS3356 announce AS-SSERV
remarks: -- AS13237 euNetworks --
import: from AS13237 accept ANY
export: to AS13237 announce AS-SSERV
remarks: -- AS42525 GlobalConnect --
import: from AS42525 accept ANY
export: to AS42525 announce AS-SSERV
So they appear to be single-homed via a small German provider and thus rather vulnerable to any general networking issue affecting SSERV, their upstreams, or their upstreams peers. Like, I dunno.. congestion or a link failure in/around Chicago. Such are the joys of BGP.
Reddit may also have some insight about their Russian woes given the reason for the block was apparently due to bomb threats made by a user. Which is one downside to 'secure' email services, ie if a State's LEOs want assistance investigating stuff like that, they may take a dim view of privacy concerns & just make the service go away. Such are the joys of 'net governance. Most countries (including Germany) have some legislation regarding lawful intercepts or just information sharing.