We apologize to the affected users for any inconvenience caused by this. The affected folders could not be accessed because the restored mails were not compatible with the current Tutanota version. By now we have cleaned the system and automatically deleted all defectively restored mails and all folders are accessible again to our users.
How was it possible that deleted mails got restored?
In Tutanota deleted mails are physically deleted, which means they cannot be restored. Due to an error in our monitoring system one hard drive defect went unnoticed. This hard drive defect led to the fact that some mail were not being physically deleted. This problem is now fixed.
Why was no data at risk of being lost?
At no point there was any data at risk of being lost. In Tutanota hundreds of million mails as well as all other content saved in Tutanota (address book) is replicated and stored several times.