Related Clues:

• Envelope stick-on
• Perforation site
• Mailing need
• If it's canceled, it's accepted
• Forever ___
• An e-mail doesn't need one
• Corner piece?
• Notary public's device
• "Forever" post office product
• Envelope stamp
• Impress with a mark
• Evidence of payment of postage duty
• Postal token
• That comes to a sticky end underfoot
• Let 'er get to put 'er foot down