Copying someone in email

Solution 1:

The Oxford English Dictionary definition 1c of the verb copy includes:

to provide (someone) with copies of correspondence, etc., on a particular subject for information. (Common in office use.)

The entry has this supporting citation from a novel published in 1983:

LaSalle pushed a file jacket across the table, and Harper flipped through the pages.‥ ‘You'll copy me on all this?’ said Harper.

So the answers to your question are that copy followed by a human direct object is established and recognised and that it has been around for almost 30 years, and possibly longer.