邮件协议

笔记参考来源：

https://www.cnblogs.com/wuyoucao/archive/2017/05/19/6880202.html 感谢作者 烦嚣的人

定义

全称是多用途互联网邮件扩展（MIME，Multipurpose Internet Mail Extensions），在MIME出台之前，使用RFC 822只能发送基本的ASCII码文本信息，邮件内容如果要包括二进制文件、声音和动画等，实现起来非常困难，最为麻烦的是多家邮件服务器商间邮件的互发，如果没有一种统一的格式定义，想要互发需要投入巨大的人力物力。MIME提供了一种可以在邮件中附加多种不同编码文件的方法，弥补了原来的信息格式的不足。实际上不仅仅是邮件编码，现在MIME经成为HTTP协议标准的一个部分。

组成

MIME消息由消息头和消息体两大部分组成。

邮件头

MIME邮件的邮件头包含了发件人、收件人、主题、时间、MIME版本、邮件内容的类型等重要信息，常见的邮件头如下：

域名	含义	添加者
Received	传输路径	各级邮件服务器
Return-Path	回复地址	目标邮件服务器
Delivered-To	发送地址	目标邮件服务器
Reply-To	回复地址	邮件的创建者
From	发件人地址	邮件的创建者
To	收件人地址	邮件的创建者
Cc	抄送地址	邮件的创建者
Bcc	暗送地址	邮件的创建者
Date	日期和时间	邮件的创建者
Subject	主题	邮件的创建者
Message-ID	消息ID 邮件的创建者
MIME-Version	MIME版本	邮件的创建者
Content-Type	内容的类型	邮件的创建者
Content-Transfer-Encoding	内容的传输编码方式 邮件的创建者

邮件类型 ContentType

表示邮件的邮件体的类型，一般以Content-Type: [type]/[subtype]; parameter 的格式出现。

type可选值如下：

type	作用
Text	用于标准化地表示的文本信息，文本消息可以是多种字符集和或者多种格式的；
Multipart	用于连接消息体的多个部分构成一个消息，这些部分可以是不同类型的数据；
Application	用于传输应用程序数据或者二进制数据；
Message	用于包装一个E-mail消息；
Image	用于传输静态图片数据；
Audio	用于传输音频或者音声数据；
Video	用于传输动态影像数据，可以是与音频编辑在一起的视频数据格式。

subtype用于指定type的详细形式。content-type/subtype配对的集合和与此相关的参数，为了确保这些值在一个有序而且公开的状态下开发，MIME使用Internet Assigned Numbers Authority (IANA)作为中心的注册机制来管理这些值。常用的subtype值如下所示：

subtype	作用
text/plain	纯文本
text/html	HTML文档
application/xhtml+xml	XHTML文档
image/gif	GIF图像
image/jpeg	JPEG图像
image/png	PNG图像
video/mpeg	MPEG动画
application/octet-stream	任意的二进制数据
application/pdf	PDF文档
application/msword	Microsoft Word文件
message/rfc822	RFC 822形式
multipart/alternative	HTML邮件的HTML形式和纯文本形式，相同内容使用不同形式表示
application/x-www-form-urlencoded	使用HTTP的POST方法提交的表单
multipart/form-data	同上，但主要用于表单提交时伴随文件上传的场合

parameter用于指定附件信息，通常用于指定text/plain和text/htm等的文字编码方式的charset参数。

默认的subtype:

type	默认值
Text	text/plain
Application	application/octet-stream
Multipart	multipart/mixed

内容传输编码 Content-Transfer-Encoding

用于指定邮件体编码，格式为 Content-Transfer-Encoding: [mechanism]，支持的值有7bit，8bit，binary，quoted-printable，base64

邮件体

邮件体内容丰富多样，既有纯文本，也有超文本、图片文字、视频、附件，那么如何表示邮件的类型？

如果Content-Type为 text/plain; charset=GBK则代表该邮件体是一个纯文本类型的邮件；但是如果邮件包含很多图片、文本、附件，则Content-Type为multipart 类型，邮件会被分为很多part(段)，每段又包含段头和段体：

MIME协议组成

所以，如果要发送一封包含附件的邮件，你的邮件的MIME类型应该为multipart/mixed

实例

纯文本：

Received: from 15616xxxxx$163.com ( [122.207.54.20] ) by
 ajax-webmail-wmsvr14 (Coremail) ; Fri, 19 May 2017 19:40:51 +0800 (CST)
X-Originating-IP: [122.207.54.20]
Date: Fri, 19 May 2017 19:40:51 +0800 (CST)
From: 15572483149 <[e-mail]>
To: [e-mail]
Subject: ss
X-Priority: 3
X-Mailer: Coremail Webmail Server Version SP_ntes V3.5 build
 20160729(86883.8884) Copyright (c) 2002-2017 www.mailtech.cn 163com
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset=GBK
MIME-Version: 1.0
Message-ID: <[e-mail]>
X-Coremail-Locale: zh_CN

我是文本内容

文本和超文本：

Received: from 15616104472$163.com ( [122.207.54.20] ) by
 ajax-webmail-wmsvr14 (Coremail) ; Fri, 19 May 2017 19:51:31 +0800 (CST)
X-Originating-IP: [122.207.54.20]
Date: Fri, 19 May 2017 19:51:31 +0800 (CST)
From: 15572483149 <[e-mail]>
To: [e-mail]
Subject:   ss
X-Priority: 3
X-Mailer: Coremail Webmail Server Version SP_ntes V3.5 build
 20160729(86883.8884) Copyright (c) 2002-2017 www.mailtech.cn 163com
X-CM-CTRLDATA: hN4rXGZvb3Rlcl9odG09ODU6NDI1
Content-Type: multipart/alternative; 
    boundary="----=_Part_214835_1240140699.1495194691872"
MIME-Version: 1.0
Message-ID: <[e-mail]>
X-Coremail-Locale: zh_CN

------=_Part_214835_1240140699.1495194691872
Content-Type: text/plain; charset=GBK
Content-Transfer-Encoding: base64

c3Nz
------=_Part_214835_1240140699.1495194691872
Content-Type: text/html; charset=GBK
Content-Transfer-Encoding: base64

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文本，超文本，附件：

Received: from 15616104472$163.com ( [122.207.54.20] ) by
 ajax-webmail-wmsvr14 (Coremail) ; Fri, 19 May 2017 20:24:26 +0800 (CST)
X-Originating-IP: [122.207.54.20]
Date: Fri, 19 May 2017 20:24:26 +0800 (CST)
From: 15572483149 <[e-mail]>
To: [e-mail]
Subject: ss
X-Priority: 3
X-Mailer: Coremail Webmail Server Version SP_ntes V3.5 build
 20160729(86883.8884) Copyright (c) 2002-2017 www.mailtech.cn 163com
X-CM-CTRLDATA: pQoIAGZvb3Rlcl9odG09ODY6NDI1
Content-Type: multipart/mixed; 
    boundary="----=_Part_217443_152692695.1495196666093"
MIME-Version: 1.0
Message-ID: <[e-mail]>
X-Coremail-Locale: zh_CN

------=_Part_217443_152692695.1495196666093
Content-Type: multipart/alternative; 
    boundary="----=_Part_217445_839318381.1495196666093"

------=_Part_217445_839318381.1495196666093
Content-Type: text/plain; charset=GBK
Content-Transfer-Encoding: base64

c2RmYQ==
------=_Part_217445_839318381.1495196666093
Content-Type: text/html; charset=GBK
Content-Transfer-Encoding: base64

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------=_Part_217443_152692695.1495196666093
Content-Type: text/plain; name="first.txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="first.txt"

MTIzNA==
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Content-Type: text/plain; name="first.txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="first.txt"

MTIzNA==
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包含所有东西：

Received: from 15616104472$163.com ( [122.207.54.20] ) by
 ajax-webmail-wmsvr14 (Coremail) ; Fri, 19 May 2017 20:37:12 +0800 (CST)
X-Originating-IP: [122.207.54.20]
Date: Fri, 19 May 2017 20:37:12 +0800 (CST)
From: 15572483149 <[e-mail]>
To: [e-mail]
Subject: ss
X-Priority: 3
X-Mailer: Coremail Webmail Server Version SP_ntes V3.5 build
 20160729(86883.8884) Copyright (c) 2002-2017 www.mailtech.cn 163com
X-CM-CTRLDATA: WqpW62Zvb3Rlcl9odG09MjUzOjM5Mg==
Content-Type: multipart/mixed; 
    boundary="----=_Part_218429_202270086.1495197432753"
MIME-Version: 1.0
Message-ID: <[e-mail]>
X-Coremail-Locale: zh_CN

------=_Part_218429_202270086.1495197432753
Content-Type: multipart/related; 
    boundary="----=_Part_218430_777936326.1495197432753"

------=_Part_218430_777936326.1495197432753
Content-Type: multipart/alternative; 
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Content-Type: text/plain; charset=GBK
Content-Transfer-Encoding: base64

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Content-Type: text/html; charset=GBK
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Content-Type: text/plain; name="first.txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="first.txt"

MTIzNA==
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