Beware of mail that is unexpected or comes from an unfamiliar sender, is addressed to someone who no longer lives or works at the address, has no return address or a return address different from the postmark, is of unusual weight, given its size, or is lopsided or oddly shaped. Also of concern: mail marked "Personal'' or "Confidential'' or mail with protruding wires, strange odors or stains. Such mail shouldn't be opened or agitated: Call police. Saying he can't yet guarantee all mail is safe, Postmaster General John Potter also urged people to wash their hands after contact.