Possible Clues:

• Opposite of c.o.d.
• Like many a reply env.
• Abbr. on a delivery slip
• Stamp not reqd.
• Remitted in advance: Abbr.
• One way to send merchandise (Abbr.)
• Like some pkgs.
• One way to send merchandise: Abbr.
• Not c.o.d.
• Rained out, e.g.: Abbr.