Exchange Server 2007传递错误（ESMTP#554 Transaction Failed Spam Message not queued#）

Anyone have ideas about this error?

Delivery has failed to these recipients or distribution lists:
[email]a@domain.com[/email]
An error occurred while trying to deliver this message to this recipient e-mail address. Microsoft Exchange will not try to redeliver this message for you. Please try resending this message, or provide the following diagnostic text to your system administrator.
The following organization rejected your message: ESMTP.
_____

Sent by Microsoft Exchange Server 2007
Diagnostic information for administrators:
Generating server: ex-serv-01.ehloex.com
[email]a@domain.com[/email]
ESMTP #554 Transaction Failed Spam Message not queued. ##
Original message headers:
Received: from ex-serv-01.ehloex.com ([10.10.1.1]) by
ex-serv-01.ehloex.com ([10.10.1.1]) with mapi; Wed, 9 Jan 2008 11:47:05
+0800
From: =?gb2312?B?zb+/odDb?= <[email]yotu@ehloex.com[/email]>
To: “[email]a@domain.com[/email]” <[email]a@domain.com[/email]>
Date: Wed, 9 Jan 2008 11:46:12 +0800
Subject: =?gb2312?B?Rlc6ILrcxua51qOsztK3otPKvP61vcTPur2jrLeisru5/cilo6y3/s7x?=
=?gb2312?B?xve08Li0yOfPwqGj?=
Thread-Topic: =?gb2312?B?utzG5rnWo6zO0rei08q8/rW9xM+6vaOst6Kyu7n9yKWjrLf+zvHG97Tw?=
=?gb2312?B?uLTI58/CoaM=?=
Thread-Index: AQHIUmgZuEXJq+62g02d7CuDpb06To0UMRlggAAOcjI=
Message-ID: <[email]C03F8E6314204C41AD2DE81F06C3A1D50E540113EA@ex-serv-01.ehloex.com[/email]>
References: <[email]9DC738C4B79E4E4C877C9D2239768E2F0D82D59A02@ex-serv-01.ehloex.com[/email]>
In-Reply-To: <[email]9DC738C4B79E4E4C877C9D2239768E2F0D82D59A02@ex-serv-01.ehloex.com[/email]>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: yes
X-MS-TNEF-Correlator:
acceptlanguage: en-US
Content-Type: multipart/mixed;
boundary=”_002_C03F8E6314204C41AD2DE81F06C3A1D50E540113EAgzmail02bingo_”
MIME-Version: 1.0