Related Clues:

• Abbr. on a business letter, perhaps
• Mailed doc.
• RSVP card, e.g.
• Business letter letters
• Ltr. add-in
• Letter-ending abbr.
• In the env.
• Something in a ltr.
• It's inside: Abbr.
• Business-letter abbr.
• It may be a copy of a ck.
• Cover letter letters
• Letter add-on (Abbr.)
• Doc. with a ltr.
• Like an SASE, often