Trying to register a new GMail address, I got the error message that the account is already in use, and I was proposed some ugly alternatives (which I did not like).
As I suspected I had used the address myself once, I send a test message to that address, waiting for a possible response.
Interestingly I got a "550" error message saying "550 5.1.1 The email account that you tried to reach does not exist. (...)"
I don't understand: If it does not exist, why can't I "take" it?
Is there any way to get some details why the particular address is unavailable?