smtp附件问题

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我在已写好的email发送程序(支持smtp认证)中加入发送,附件 功能.
根据mime 1.0构发邮件并发送.但发现不对.请高手指教.
我的编码后的邮件为:
From: [e-mail]
Date: Thu, 19 Jul 2001 10:55:22 -0600
X-Mailer: BigAnt Smtp Mailer V1.0
To: [e-mail]
Subject: for send mail test
MIME-Version: 1.0
Content-type:multipart/mixed;
boundary ="----=_NextPart_000_000A_01BF9F1A"

------=_NextPart_000_000A_01BF9F1A
Content-Type: text/plain;
Charset = "gb2312"
Content-Transfer-Encoding: 8bit

do you get the test mail

------=_NextPart_000_000A_01BF9F1A
Content-Type: Application/octet-stream
name=d:\Email&FaxJob\Email\a.txt
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
FileName=d:\Email&FaxJob\Email\a.txt

T24gY2VydGFpbiB0eXBlcyBvZiBzbWFsbGVyIG5vZGVzIGluIHRoZSBJbnRlcm5ldCBpdCBp
cyBvZnRlbg0KICAgaW1wcmFjdGljYWwgdG8gbWFpbnRhaW4gYSBtZXNzYWdlIHRyYW5zcG9y
dCBzeXN0ZW0gKE1UUykuIA==
------=_NextPart_000_000A_01BF9F1A--


用outlook收取后.同上,连subject这个field不解.为什么.
为什么有Content-Disposition: attachment;,不会被解为附件呢.