How to distribute session keys in public key cryptography?
Normally, the client sends the session key.  This means that clients cannot decrypt other session keys.

Although this approach ensures each session is safe from information gathered in other sessions, it doesn't guard the session against an attacker later acquiring the server's key and retrospectively decoding all recorded sessions.

To guard against that threat is termed Perfect Forward Privacy.  This can be achieved using ephemeral Diffie-Hellman (EDH,DHE) key exchange.

There is an excellent blog explaining recent improvements in Perfect Forward Secrecy which is well worth reading.