Hello Carsten
Sorry I couldn't find time to dig more on this until now.
Now I have Icedove 45.1.0 in Debian stable.
I tried to add your custom header X-Special-Xy and it worked.
Then I tried to add a custom header called X-Approved and it worked.
Then I tried to add a custom header called Approved (the one I need) and
it breaks the headers.
I tried also with "approved" and it also breaks the headers.
I tried both using the config editor, and also creating a "user.js" file
in my profile with the line:
user_pref("mail.compose.other.header", "Approved");
Hope that helps
--
Laura Arjona
https://wiki.debian.org/LauraArjona
