We are very sorry about this inconvenience. We are already in contact with our registrar, who promised to update our DNSKEY as soon as possible. We hope that something like this will never happen again.
Currently only users accessing Tutanota via a server that supports DNSSEC experience problems. If you cannot connect to Tutanota, you can switch your connecting server as a work-around, ie by using a VPN. Users have told us that it is possible to access Tutanota via Freedom VPN, PIA, Shellfire and ZenMate.
Update October 22nd: As of last night, the new DNSKEY was rolled out to all servers so that Tutanota is available again around the world.
We currently have an uptime of 99,99%. However, even a partial downtime to some users - as this one - is not at all tolerable. Therefore, we would like to apologize to all affected users. We also plan to improve the notification message when you can't reach our server so that you can better understand the cause.