Change location of pop-up for new message window

I have pop-up notification enabled: a small window will show the subject, sender, text of a new message. This window used to be in the lower right corner of the monitor above the windows tray, no matter where my mouse or cursor was while working (good). Recently, this pop-up window appears where my mouse (?) is - so positioned completely "random" on the monitor. (TB 78.11.0 32 BIT) In the options I can choose if to display a window at all (yes), what it should include and how long to display. But there is no way of changing the location back to "do not follow mouse". --> How can I put it back in a fixed position?