At the top click "extras" >"Edit Options.
Then Scroll down to the "Messaging & Notification" part and find the block. Click the arrow going down and choose "Do Not Subscribe".
Also scroll down a little more but still in the "Messaging & Notification" part and and delete the check mark in the part that says "Receive Email Notification of New Private Messages" to stop emails of PM notification.
Here you can also...
edit getting messages from other members and admins.
Disable you PM system