@Fcasoli -- thank you.
I've added the necessary spaces -- they're the same in every language -- it's the Italian (and French and German....) words that are difficult for me
On message-id:
There is already a setting for the "User-Agent" header. Both "User-Agent" and "Message-ID" are specific technical term, it's not "some kind of message identification", but rather "the Message-ID header defined for Internet mail".
The setting for "User-Agent" is like this:
<string name="prefs_compose_user_agent">Invia \"User-Agent\"</string>
<string name="prefs_compose_user_agent_summary">Aggiungi \"User-Agent header\" durante l\'invio di un messaggio</string>
Would this be ok for "Message-ID"?
<string name="account_options_prefs_outgoing_message_id">Invia \"Message-Id\"</string>
<string name="account_options_prefs_outgoing_message_id_summary">Aggiungi \"Message-Id header\" durante l\'invio di un messaggio</string>