Related Clues:
- Postal abbr
- 5-Across's business
- Word with "snail" or "chain"
- Env. stuffing
- S.A.S.E., e.g.: Abbr
- Letters delivered
- It's signed, sealed and delivered
- Junk __
- Postal Service delivery
- Env. within an env., perhaps
- Inbox stuff
- Mother not well missing little metallic dress of armour
- It may be registered or certified
- Some airplane cargo
- Armor of a sort