Ask if you can FAX it as that is safer.
IMnsHO, the method of
delivery is of distantly secondary concern. Of much greater concern is protection and limitation of the information within the document.
It is understandable and reasonable to request (indeed, require) some form of identification to verify that the individual is real and not just fictitious.
That being said, it is both unwise and unnecessary to provide
excessive information that can be abused in the future in potential identity theft attempts.
Remember, you have absolutely no control over who might obtain the information in the future, even if the
initial recipient is honest and of pure intent.
Sure, by all means send them a photocopy of your driver's license by mail or fax, but redact (black out) the license number and your date of birth first.
Tell them if they really need those unnecessary details, they can obtain them directly from the RMV (which certainly won't release that info either, btw).
They need to know that you really exist and have an address ---
that's all. They don't need (and are certainly not entitled to) any irrelevant and unnecessary personal details or information beyond that which is required to verify your existence. Be smart --- protect your personal information.