string eml = File.ReadAllText("c:\\mia.eml");
            string subject = string.Empty;

            Regex regex = new Regex("Subject:(.*)", RegexOptions.Multiline | RegexOptions.IgnorePatternWhitespace |  RegexOptions.IgnoreCase);
            if (regex.IsMatch(eml))
                subject = regex.Match(eml).Groups[0].Value;