[jcape]

Typically those sorts of things are required for compliance purposes.

Stockbrokers (broker-dealers) are required by the SEC to record all text-based electronic communications, keep 7 years worth of backup on write-once, read-many media (e.g. DVD), and upload copies to a third party (to prevent "sorry, sir, the dog ate all the emails where the traders were talking about rigging LIBOR"-style excuses).

I assume there's something similar for US-listed companies, thanks to Enron.