Related Clues:

• Abbr. on the bottom of a business letter
• Something in an env
• Britannica, for one: Abbr
• Check within, say?: Abbr
• Inside, for short
• Postal abbr
• S.A.S.E., e.g.: Abbr
• Env. within an env., perhaps
• Pkg. insert
• Postal letters
• Letter abbr
• Cause of an env. bulge
• Ltr.-bottom letters
• Ref. wk
• In the env