Function matching 

fn matching<'a>(
    config: &'a Config,
    server: &str,
    login: &str,
    user: Option<&str>,
) -> Option<&'a Account>

Your contacts-and-calendars account for that server and login, if there is one (switched off ones too): its address on the server’s origin (on_server: scheme, host and port, never the host’s name alone, which Accounts keeps without its port), with the same login (case aside) or the same user in its address (user_of). Google’s are never.