mail-notification popup notifications aren't working.

>From terminal:
$ mail-notification &
libnotify-Message: Unable to get session bus: Failed to execute
dbus-launch to autolaunch D-Bus session

And this dialog:
An initialization error has occurred in Mail Notification
Unable to initialize the notification library. Message popups will not
be displayed.

Any ideas what's causing this?

Cheers,

Lex.