这又是什么原因引起的退信？？请高手帮忙，急！！！

your615

----- Original Message ----- <br>
From: "Mail Delivery Subsystem" <MAILER-DAEMON@mail5.atl.registeredsite.com><br>
To: <Ａ@Ｂ.com><br>
Sent: Thursday, September 22, 2005 12:12 AM<br>
Subject: Returned mail: see transcript for details<br>
<br>
<br>
> The original message was received at Wed, 21 Sep 2005 12:11:54 -0400<br>
> from novotelapollo.com [209.203.239.110]<br>
> <br>
> *** ATTENTION ***<br>
> <br>
> This email is being returned to you because the remote server would not<br>
> or could not accept the message. The registeredsite servers are just<br>
> reporting to you what happened and are not the source of the problem.<br>
> <br>
> The address which was undeliverable is in the section labeled:<br>
> "----- The following addresses had permanent fatal errors -----".<br>
> <br>
> The reason your mail is being returned to you is in the section labeled:<br>
> "----- Transcript of Session Follows -----".<br>
> <br>
> This section describes the specific reason your e-mail could not be<br>
> delivered.<br>
> <br>
> Please direct further questions regarding this message to your e-mail<br>
> administrator.<br>
> <br>
> --Registeredsite Postmaster<br>
> <br>
> ----- The following addresses had permanent fatal errors -----<br>
> <Ｃ@Ｂ.com><br>
> (reason: 530 Authentication required)<br>
> <br>
> ----- Transcript of session follows -----<br>
> ... while talking to Ｂ.com.:<br>
>>>> RCPT To:<Ｃ@Ｂ.com><br>
> <<< 530 Authentication required<br>
> 554 5.0.0 Service unavailable<br>
<br>
<br>
我的服务器有要求ＳＭＴＰ认证，发其它都没这种退信．是什么原因，请高手帮帮忙，先谢了．