in GPL FAQ there is this statement just after the notice example:
Also add information on how to contact you by electronic and paper mail.
I don't understand if this is mandatory, since in the notice states you must only insert the year and the author name and surname.
I note that the text you quote doesn't appear in the GPL FAQ, but comes from the advice section at the end of the GPL entitled "How to Apply These Terms to Your New Programs". This section, as I understand it, is a collection of best-practice advice on publishing your code under the GPL, rather than a set of legal requirements. You don't even have to include your real name, or a copyright notice, if you don't want to: the real core of the advice is to make it unambiguously clear to potential users that they are receiving the code under a particular version of the GPL, so they know what their rights are.
The only binding exception I can think of is if you're distributing code which is based on someone else's GPL-covered code, and which is "baked into" a physical product, and you are not distributing source at the same time (a section 6(b) distribution, according to GPLv3). In this case, the product must be
accompanied by a written offer, valid for at least three years and valid for as long as you offer spare parts or customer support for that product model, to give anyone who possesses the object code either (1) a copy of the Corresponding Source for all the software in the product that is covered by this License, on a durable physical medium customarily used for software interchange, for a price no more than your reasonable cost of physically performing this conveying of source, or (2) access to copy the Corresponding Source from a network server at no charge
If this applies, then I think one of your consequent obligations is to give real, current, and durable contact details so that someone who wishes to take you up on the offer can do so.
