I cannot ask any mail service to break the law (and jeopardize their own families, businesses, etc) just to protect my data. If Posteo is legally served a warrant, I expect them to comply with the legally authorized authorities. HOWEVER, all they can turn over is my encrypted data, because my account is set to automatically encrypt all saved data. Period. If the authorities want to waste their time and energy trying to decrypt that data (of which, only I posses the encryption keys), then have at it - they’ll be super disappointed (and really bored) by whatever they find, but whatever.