They are called Private Messages.
To access them
1. Log onto Radio Reference
At the right hand top of the page you will see the following boxes:
My forum Threads and then Private Mesg
Click on the Private Mesg link.
This will take you to another page, from there you will scroll down and click on the link and that will open the private message which you can read.
You also have the option to reply back to the Private Message if you like.
Private messages are like emails through RadioReference
If you have anymore trouble just let me know
David