Intra-corporate e-mail is often used as an ad hoc document collaboration tool.
"See my comments in blue", strikethroughs, inline diagrams, bullet points, big red font for emphasis.
Of course that should all be done in a dedicated application, but who is going to provision and authorise users for that versus just adding Bob to the cc line and giving him implicit editing capabilities?
The functional overloading of corporate e-mail is a user-driven reaction to the awfulness of most " collaborative' software.
