Though no new mailbox bombs have been found in Iowa since they were first discovered Friday, the U-S Post Office is taking no chances. Arlington postmaster James Clapp says delivery depends on leaving your curbside mailbox open today.He says letter carriers won’t put mail in a box if its door is closed, for the safety of both customers and carriers. Clapp says the rule is not just for country postal customers, either. Even inside city limits, they won’t deliver. City customers with mailboxes out at the side of the street must leave the door open, like rural mail recipients. The only ones that don’t have to be left wide open are mail containers attached to a house, or the multiple apartment-style mailboxes that are all locked with a key.