The PROPID_M_DEST_SYMM_KEY property specifies the symmetric key used to encrypt messages.
This property is used when sending encrypted messages to a foreign queue. The symmetric key is encrypted with the public key of the receiving Queue Manager.
When a connector application receives an encrypted message, it forwards the encrypted message with the attached symmetric key to the receiving application. It is the receiving application's responsibility to decrypt the symmetric key and the body of the message.
MQReceiveMessage, PROPID_M_DEST_SYMM_KEY_LEN