I got the idea from some shareware programs that require sending a postcard to the author for registration. As explained above, I can't keep the web site open to everyone, but it seems a waste to have the web site sitting there with no one allowed to use it. So I needed a way to cut traffic dramatically, and that's what the postcard requirement does.
I know that the postcard requirement is inconvenient. My goal is not convenience. I don't really want people to use my site unless there is no other choice. At the same time, I want to make it possible for people to access the site if they really have no other choice.
No.
Yes, I will accept letters, but a postcard is preferred.
You don't have to put your mailing address on your postcard, if you don't want to. You do have to put your e-mail address on the postcard--if you don't want to give out your e-mail address, sign up for a free throwaway account on Yahoo or something.
All material sent by the postal service bears a postmark identifying the city of origin. If you're concerned about giving out what city you live in, then mail your postcard from a different city.