1. bearing an official postal mark showing the date and place of mailing

Examples

• The letter was postmarked December 15th from Chicago.
• All postmarked envelopes must be received by the deadline.
• The package arrived with a clearly postmarked label.
• She kept the postmarked envelope as proof of when she sent it.
• The postmarked mail was sorted by date at the post office.
• His application was postmarked just before the cutoff time.