So NSA read corporate emails too?
Of course.
According to the Snowden leaks, the aim of the NSA isn't to just collect information on terrorist threats to the nation, their aim is to collect information that is "beneficial" to the nation. If a corporation foreign or domestic has information that is useful they will collect it and use it, whether it be financial records, source code, or blueprints for new inventions.
http://www.liveleak.com/view?i=f93_1390833151