not sure how e-mail encryption would have helped... ? They SQL injected and got the DB, obtained the passwords and then proceeded further (social engineering: FW policy change, ssh password through e-mail, etc.)
Also, a common policy of encrypting and signing emails would have stopped the social engineering attack completely, as the sysadmin would've known not to accept an unsigned request to give out passwords.
Kind of mind boggling that people don't do this generally already.