Sam,
it works like this:
Each GC has a unique "code" like "5732778865429" (no need to try it, it's a used one

), and is connected to the giver's e-mail-address. With these two bits of information, it can be redeemed by anyone with a Kiva account.
You can either send "the GC" and this information to the recipient through Kiva, or send an e-mail of yourself, or even give these information to the recipient on paper (like the printed out version of the GC that looks reasonably well) or over the phone...
So it does not really matter whether you enter the correct recipient's e-mail; as long as the "true" recipient gets these two bits of information (code and e-mail of giver), everything is fine. Of course, if you enter a wrong e-mail-address for the recipient, it could happen that someone else gets hold of the information and makes use of it before the intended recipient - I don't know how Kiva would deal with such a case.
Hope to help, best wishes,
Wolfgang.
****
PS: Geoff was faster, and his explanation is better. So - sorry for saying it all again.