a <#postalmark=postal marking>, usually applied to the back of a <#cover>, evidencing either the arrival of a cover at its destination post office or the handling of a cover while in transit. Applying a backstamp to <#firstclass=First Class Mail> upon arrival at the destination post office was mandatory from 1879 until 1913. The backstamping of ordinary air mail was discontinued in 1929. See <#receiving=Receiving Mark> and <#tranmark=Transit Mark>.