Related Clues:

• Passport feature
• Email doesn't require one
• ___ of approval
• It shows date and time of mailing
• Postage buy
• Amtrak bullet train
• Notary need
• Appropriate star of "The Collector"
• It's often stuck in the corner
• It can be used in dating
• Word after "rubber" or "time"
• Postage item
• Put one's foot down, as a matter of duty
• Snail-mail attachment
• Official mark; bang (foot)