I think I remember that PGP did (does?) it this way ... since Public Key cryptography was (is?) very computationally expensive for large messages.
It created a large, one-time key to symmetrically encode the main (presumably long) message. The key was "randomly" created based on mouse movements or something on the sender's PC. The one-time key was encrypted using the recipient's Public Key and the main message encrypted by the one-time key. The two were combined and transmitted together.
Only the recipient's Private Key could decrypt the one-time key which was then used to decrypt the main message.