smtp协议

一、smtp命令

1、HELO　向服务器标识用户身份

2、MAIL　初始化邮件传输mail from: <xxx>

3、RCPT　标识单个的邮件接收人；常在MAIL命令后面可有多个rcpt to: <xxx>

4、DATA　在单个或多个RCPT命令后，表示所有的邮件接收人已标识，初始化数据传输，以.结束

5、NOOP　无操作，服务器应响应OK

6、RSET　重置会话，当前传输被取消

7、QUIT　结束会话

二、邮件内容: 首部+正文

首部：

FROM：<姓名><邮件地址> 邮件发送者。

TO：<姓名><邮件地址> 邮件接收者。

CC：<姓名><邮件地址> 邮件抄送者。

SUBJECT：<邮件标题> 邮件密送者。

DATE：<时间> 发邮件的时间。

REPLY-TO：<邮件地址> 邮件的回复地址。

Content-Type：<邮件类型> 表明邮件包含文本、HTML超文本和附件的哪些类型，邮件包含多种类型时需分别指定类型。

MIME-Version：<版本>，MIME的意思是Multipurpose Internet Mail Extensions，即多用途Internet邮件扩展标准，它对传输内容的消息、附件及其他的内容定义了格式。

正文：

邮件正文

MIME段头 

MIME内容

三、正文例子

---------------------------------------------------------------------------------------------------------首部----------------------------------------------------------------------------

            "From: from@example.com " +
            "To: to@example.com " +
            "Content-Type: multipart/mixed; boundary=_BOUNDARY_1_ " +                            ---------multipart1  
            " " +
            "--_BOUNDARY_1_ " +
            "Content-Type: multipart/related; boundary=_BOUNDARY_2_ " +                           ---------multipart2
            " " +
            "--_BOUNDARY_2_ " +
            "Content-Type: multipart/alternative; boundary=_BOUNDARY_3_ " +                      ---------multipart3
            " " +
            "--_BOUNDARY_3_ " +
            "Content-Type: text/plain; charset=UTF-8 " +
            "Content-Transfer-Encoding: quoted-printable " +
            " " +
---------------------------------------------------------------------------------------------------------内容---------------------------------------------------------------------------------           

　　　　"=C2=A1Hola, se=C3=B1or! " +
           

　　　　 "--_BOUNDARY_3_ " +                                                                                      -----------multipart3 MIME段头
            "Content-Type: text/html; charset=UTF-8 " +                                                      ----------html 文本内容
            "Content-Transfer-Encoding: quoted-printable " +
            " " +
            "=C2=A1<b>Hola</b>, <i>se=C3=B1or</i>!</h1> " +                                       ----------multipart3  MIME内容
            "--_BOUNDARY_3_-- " +
            " " +
            "--_BOUNDARY_2_ " +                                                                                      -----------multipart2 MIME段头
            "Content-Type: image/jpeg; name="image.jpg" " +
            "Content-Disposition: inline; filename="image.jpg" " +                                        -----------inline 正文内嵌图片
            "Content-ID: <image.jpg> " +
            "Content-Transfer-Encoding: base64 " +
            " " +
            base64.StdEncoding.EncodeToString([]byte("Content 2")) + " " +                         ----------multipart2  MIME内容
            "--_BOUNDARY_2_-- " +
            " " +
            "--_BOUNDARY_1_ " +                                                                                     -----------multipart1 MIME段头
            "Content-Type: application/pdf; name="test.pdf" " +
            "Content-Disposition: attachment; filename="test.pdf" " +                                -----------attachment表明为附件
            "Content-Transfer-Encoding: base64 " +
            " " +
            base64.StdEncoding.EncodeToString([]byte("Content 1")) + " " +                        ----------multipart1  MIME内容
            "--_BOUNDARY_1_-- ",