http://fmrdomwz63365ly7qy5fdcjjs3manv4dkl3vr6imwfd5dxyuonia.b32.i2p/asymmetric-encryption
Someone proposed an ingenious solution: after your friend receives it, he can use his own lock to secure it again and mail it back to you. After you receive it, you unlock your lock with your key and mail it to him again. Finally, he uses his key to unlock his lock and then he can read it.