What should you do if you suspect a letter or parcel is dangerous?

If you suspect a letter or parcel to be dangerous, the appropriate action is to contact local military law enforcement officials. This is because they have the training, resources, and protocols in place to safely handle potentially hazardous materials. They can assess the situation, investigate, and take necessary precautions to ensure public safety.

Opening the item could expose you to harmful substances or devices, and leaving it in the mailbox might not mitigate the risk, as it could still pose a danger to others. Sending it back to the sender is not advisable either, as it does not address the immediate potential threat and could further endanger others involved in the process. Therefore, notifying the authorities is the best course of action.