postmark
noun [ C ]
COMMUNICATIONS uk/ˈpəʊstmɑːk/ usan official mark put on a letter or package, showing the place that it was sent from and the time or date that it was sent:
Twenty-four letters were delivered with a Washington D.C. postmark.
postmark
verb [ T/usually passive ]
uk/ˈpəʊstmɑːk/ usto put an official mark on a letter or package, showing the place that it was sent from and the time or date that it was sent:
be postmarked Applications must be postmarked by Oct. 1.