Postmarking by a date means??

Question

Letters must be postmarked by the due date of March 1, or the application will not be accepted.

Does this mean I must get it stamped by the post office by March 1? It doesn't mean it has to get to the receiver on March 1, right? Just sent and stamped by the post office by March 1.

Answer 1

You're correct. It means that it must have been stamped by the post office, to prove that if it gets there late, then it wasn't due to your being late sending it, but due to the mail service messing up.