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