why my emails go to junk mail :(

[eluser]Sumon[/eluser]
@cahva : i don't find anything like X-Spam-Status or even score. Here is my full header(from yahoo mail)

Code:

From Manktech Corp Thu Apr 23 08:31:23 2009
Return-Path: <[email protected]>
Authentication-Results: mta454.mail.re4.yahoo.com  from=manktech.com; domainkeys=neutral (no sig); from=manktech.com; dkim=neutral (no  sig)
Received: from 67.212.190.3  (EHLO host1.internethostserver.com) (67.212.190.3)
  by mta454.mail.re4.yahoo.com with SMTP; Thu, 23 Apr 2009 01:31:26 -0700
Received: from nobody by host1.internethostserver.com with local (Exim 4.69)
    (envelope-from <[email protected]>)
    id 1LwuL5-0005Vj-7N
    for [email protected]; Thu, 23 Apr 2009 04:31:23 -0400
User-Agent: CodeIgniter
Date: Thu, 23 Apr 2009 04:31:23 -0400
From: "Dinga" <[email protected]>
To: [email protected]
Subject: Email Test using CI
Reply-To: "[email protected]" <[email protected]>
Message-ID: <[email protected]>
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Content-Length: 25

@cahva: nop you are wrong. it works fine with gmail and hotmail address. all recipient get mail at inbox except yahoo.
i am not sure my header is fine or not. how can i test my header is ok.

guys Big thanks to you all. you are really helping me
and sorry for my bad english