1. an official mark stamped on mail by a post office, showing the date and place of mailing

1. to stamp mail with an official mark showing the date and place of mailing

Examples

• The postmark on the envelope showed it was mailed from Chicago.
• I could barely read the smudged postmark on the old letter.
• The package had a postmark dated three days ago.
• Make sure to postmark the application before the deadline.
• The postal worker will postmark your letter when it’s processed.
• She collected stamps with interesting postmarks from around the world.
• The postmark proved the letter was sent on time.