In an error case, Tutanota clients display an error message and provide a function to send the error details to our support. These error details never contain any personal data (e.g. no ip addresses) and are used by our support for tracking down the error that occurred on a client.
We also log technical info, warning and error messages on the server side. These messages never contain any personal data and are also used for improving Tutanota. These logs are kept for 7 days.