@Tutanota You could make it even easier by adding a feature that others have. This would also save you storage and power in the long run.

Rules should be able to be configured with a delay and exception.

Example: Emails from jonas@example.com will be moved to the folder Trash after 730 days except when labeled "Wedding plans".

Gmail and Proton (and anyone who supports the client Thunderbird) allows exceptions for "starred" emails but I imagine specific labels or any labels could be about as user friendly.