By default, Private Messaging (PM) is enabled for all members. You may not wish to send or receive PMs. The answer is to disable the PM feature for your account.
Step 1.) Click on the "My Stuff".
Step 2.) From the "My Stuff" drop-down menu, choose "Edit Preferences."
Step 3.) Select "No" under the question "Accept private messages from other users?"
Step 4.) Click the "Submit" button to save your changes.
Step 5.) There is no Step 5!!! It's that easy!
To re-enable the PM feature on your account, follow these same instructions but choose "Yes" instead of "No" in Step 3.
Note that you will still receive official PM communications from Administrators and Moderators should it become necessary to contact you.