Dear K., I apologize for saying something so absurd. It is the private Gmail account of one of the conference organizers, who of course are obliged to respect all pricacy regulations. You can ask the organizing team at any time for the confirmation of that address.

Of course, however, your certificate of attendance can include nothing but your name -- nobody is compelled to share their address if they don't want to.

I hope this was helpful!
Friendly regards,

Michele