What is the ruling on postal mail that contains what is wrong?

A questioner asks and says: Your Eminence, Shaykh Ibn Baz (may Allah grant him success), I am an employee at the post office. Sometimes envelopes arrive that contain singing tapes and obscene pictures. Is this a trust that I must deliver, or should I destroy it without the knowledge of the supervisor and without the knowledge of the sender? Please inform us, may Allah reward you with good.
This is the example that should be mentioned. Destroying something like this is not betrayal of trust; rather, it is fulfilling a trust. If you know that this envelope contains what Allah has forbidden and a call to what Allah has forbidden, it is obligatory to destroy it. Destroy the corrupt tapes that call to falsehood and the corrupt pictures that call to falsehood, without needing to seek permission from the supervisor. If you know this and examine it, it is obligatory to destroy it, because this falls under the category of forbidding what is wrong. Delivering it to its owner is betrayal of trust, not fulfilling a trust.