Bewertet mit 3 von 5 Sternen

I've installed the addon in Postbox, I have inserted the API key, but doesn't work in the sense that the information don't appear in the message. Do I need to make some additonal configuration?

Diese Bewertung wurde für eine vorherige Version des Add-ons (2.0.0) abgegeben. 

Postbox is a bit different, the MailHops data is in the sidebar (or inspector pane), not the message. Open the Inspector Pane by going to View > Show > Inspector Pane (Shift + Command + I)