I work for a government agency. ANY email or other written communication could become public record. Therefore, if in doubt, do not write it. If it's sensitive, we discuss it behind closed doors and it stays there. The same was true when I worked in the defense industry.
If you want to send private emails, you should use a private account and in some instances that may be against policy. Companies and governments have the right to set rules. They can and will enforce them if needed. I've seen it happen more than once.
Keep Up with TechRepublic