Since everyone needs a dubious scientific law named after them, here’s my attempt at formulating one. Enjoy.
“The degree to which a piece of correspondence is of importance is indirectly proportional to the degree to which it is said to be ‘urgent’ by its sender.”
Or if you prefer:
“The importance of an e-mail’s content is indirectly proportional to the number of exclamation marks which appear in the subject box.”