try  string s = @"From: aaaaaaaaaaaa          aaaaaaaaaaaa
baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
caaaaaaaaaaaad
To: bbbbbbbbbbbbbbbbbb      bbbbbbbbbbbb
        bbbbbbbbbbbbbbbbbb
";   Regex r = new Regex("From:(?<from>.*(\n\t.*)*(?=\n\\S|$))", RegexOptions.IgnoreCase);
   Match m = r.Match(s);
   if (m.Success)
Console.WriteLine("{0}",m.Groups["from"].Value);