x-add-key fails for inline key material followed by non-key material like a signature
x-add-key fails for users sending mails with an ascii-armored key, followed by non-key material, for example a signature included in the body.
The code of self.is_armored_key?(material) in lib/schleuder/plugins/key_management.rb needs to be more specific to only capture the relevant parts of the body.