Related Clues:

• Env. insertion
• Bus. letter attachment
• Collier's work: Abbr.
• Ltr. accompanier
• Ref. set
• 5 Placed inside: abbr.
• SASE, for example
• What's inside an env.
• Ltr. extra
• In this env.
• Something besides the ltr.
• Mailed doc.
• RSVP card, e.g.
• Business letter letters
• Letter-ending abbr.