Related Clues:

• Envelope stick-on
• Perforation site
• Mailing need
• If it's canceled, it's accepted
• Forever ___
• High-speed Amtrak train
• An e-mail doesn't need one
• Corner piece?
• Notary public's device
• Boston-DC connection
• Fleet Amtrak train
• "Forever" post office product
• Rapid Northeast train
• Impress with a mark
• Evidence of payment of postage duty