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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：

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 <15616xxxxxx@163.com>
To: 272xxxxx5@qq.com
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: <c756733.d8f8.15c2082a579.Coremail.1561610xxxx@163.com>
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 <1561610xxxx2@163.com>
To: 272xxxxx5@qq.com
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: <10858dc0.d9be.15c208c6920.Coremail.15616xxxx2@163.com>
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

PGRpdiBzdHlsZT0ibGluZS1oZWlnaHQ6MS43O2NvbG9yOiMwMDAwMDA7Zm9udC1zaXplOjE0cHg7
Zm9udC1mYW1pbHk6QXJpYWwiPnNzczwvZGl2Pjxicj48YnI+PHNwYW4gdGl0bGU9Im5ldGVhc2Vm
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c3A7ICZuYnNwOzwvZGl2PjwvZGl2Pjwvc3Bhbj4=
------=_Part_214835_1240140699.1495194691872--

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 <15616104472@163.com>
To: 2728474645@qq.com
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: <60b56d3.dc89.15c20aa88ed.Coremail.15616104472@163.com>
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

PGRpdiBzdHlsZT0ibGluZS1oZWlnaHQ6MS43O2NvbG9yOiMwMDAwMDA7Zm9udC1zaXplOjE0cHg7
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------=_Part_217445_839318381.1495196666093--

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

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

MTIzNA==
------=_Part_217443_152692695.1495196666093--

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 <1561xxxxxx@163.com>
To: 1561xxxxxx@163.com
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: <6b289d2b.dd97.15c20b63bb1.Coremail.15616xxxx2@163.com>
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; 
    boundary="----=_Part_218431_95247708.1495197432753"

------=_Part_218431_95247708.1495197432753
Content-Type: text/plain; charset=GBK
Content-Transfer-Encoding: base64

c2Rm
------=_Part_218431_95247708.1495197432753
Content-Type: text/html; charset=GBK
Content-Transfer-Encoding: base64

PGRpdiBzdHlsZT0ibGluZS1oZWlnaHQ6MS43O2NvbG9yOiMwMDAwMDA7Zm9udC1zaXplOjE0cHg7
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------=_Part_218431_95247708.1495197432753--

------=_Part_218430_777936326.1495197432753
Content-Type: image/png; name="circle.png"
Content-Transfer-Encoding: base64
Content-Disposition: inline; filename="circle.png"
Content-ID: <42ea7473$2$15c20b63bb1$Coremail$15616104472$163.com>

iVBORw0KGgoAAAANSUhEUgAAADAAAAAwCAQAAAD9CzEMAAAABGdBTUEAALGPC/xhBQAAACBjSFJN
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------=_Part_218430_777936326.1495197432753--

------=_Part_218429_202270086.1495197432753
Content-Type: text/plain; name="first.txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="first.txt"

MTIzNA==
------=_Part_218429_202270086.1495197432753--
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