Related Clues:

• Business-envelope abbr
• End-of-letter abbr
• Business letter abbr
• Insert of a sort: Abbr
• Mail-routing abbr
• Abbr. before some addressees
• Britannica, for one: Abbr
• Letters followed by a colon
• Start of a memo heading
• Business env. letters
• Env. stuffing
• S.A.S.E., e.g.: Abbr
• Routing abbr
• Pkg. insert
• Fax abbr