How can you see if someone has read a PM?

[Nella]

Is it possible to see in 'My messages' that the person you have send a PM to have read it?
Or not?

On other forums I'm used to be able to see if the PM is opened or not. But I haven't figured out how it works over here .

[Kiwi]

My Messages -> Sent Items

There is a little envelope icon next to each message - if the flag is up, the message has been read (ie open envelope). If the flap is down, the message has not been read (ie closed envelope).