I had email address X (gmail) that I hadn't logged into for a long time. One day I tried to log in to it. Correct password, but Google, for some reason, simply decided there's something suspicious about my login and blocked it. X had Y as the "recovery email", and I had access to Y, and I indeed received an email from Google sent to Y that it blocked a suspicious login to X. However, THERE WAS NO WAY TO USE Y TO GAIN ACCESS TO X. Google simply did not offer that option for X, and I had no idea why.