Yup, thanks for keeping me honest!   I don't know what's wrong today - must be a full moon.  The public and private keys both share a common modulus, which is used in both the encryption and decryption process; therefore the receiver only needs the private key to decrypt the message.

For secure e-mail, are you talking about PGP?  If I recall correctly, PGP uses symmetric encryption to encrypt a message, and then uses asymmetric public-key encryption to encrypt the symmetric key, which is then sent with the message.

Thanks!