Bewertet mit 1 von 5 Sternen

Broken on 78.11.0 where the header completely disappears when enabled. Disabling the plugin does restore the header. Previous version worked well

Diese Bewertung wurde für eine vorherige Version des Add-ons (2.20) abgegeben. 

If it doesn't show any headers at all, you possibly clicked "Hide Headers".
Try right clicking a message or the message list and select "Show Headers" near the bottom.
There is also a menu item: View > Headers > Show/Hide Headers.