Exit in Envelope Market

The Wall Street Journal reports that envelope maker "National Envelope Corp." will file for bankruptcy.  Given the increase in the demand for email (which is a substitute for letters) this results in a decrease in the demand for letters.  Since envelopes are a complement to letters, the decrease in the demand for letters results in a decrease in the demand for envelopes (volume or quantity has been falling between 3% and 4% annually since 2001), which is a driving force for National Envelope Corp.'s bankruptcy filing.