The post office uses a couple of methods to check packages they handle.. . They use x-ray, metal detection, chemical sniffers, trained dogs, etc. depending upon their local budget and their known problems in the past. . . They have the right to open any mail they suspect to be a problem even if no alarms went off.. . You cannot sent mail to a person who's name is grandma or uncle, etc. You must use a valid name and address. Otherwise it will not be sent.