一说写代码发邮件，好多人第一反应就是找开源库。其实看下smtp协议还是挺简单的，不简单哪对得起那个s呐。以我个人的理解这里主要有以下几个基本命令：
| helo | hostname交换，对付垃圾邮件时dns反查会用到 |
| ehlo | 比helo返回信息多些，如支持的登录认证方式、最大邮件尺寸等等 |
| auth | 请求服务器认证，参数为认证方式。现在一般的邮件服务器都要求认证后才能发信，如auth login后要依次发送username、passwd的base64字符串到服务器，完成login认证 |
| mail from: | 提交发件人地址，要求与auth的username对应 |
| rcpt to: | 提交收件人地址 |
| data | 开始邮件内容 |
| \r\n.\r\n | 结束data输入 |
| quit | 退出与服务器的会话 |
有了这些就可以发送普通基本的文本邮件了。
当然，对于更丰富的内容这点东西就显得有些单薄了。
这时就需要MIME（Multipurpose Internet Mail Extensions 多功能Internet 邮件扩充服务）的扩展支持了。本着以实践应用为目的指导思想来说，这里需要的mime就是遵循mime的标准，把电子邮件切成多个部分，分别表示文本内容和二进制内容（附件）。至于具体怎么切呢，主要有下面几个基本字段需要说明：
| MIME-Version | mime版本 |
| Content-Type | 内容数据类型 |
| Content-Transfer-Encoding | 数据编码方式，如7bit，8bit，base64等等 |
| Content-Disposition | 这里决定是否在行内显示附件或作为单独的附件 |
| boundary | 定义内容边界，一个唯一字符串，使用时要在前面加两个横杠 |
嗯，有了这些，就可以按照如下格式构建稍微不那么简单点的smtp会话了
#include <iostream>
#include "tns.h"
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#define PORT 25
#define HOST "smtp.sina.com"
const char *msg[]={
"ehlo mailer.com\r\n",//与服务器交互hostname，用作垃圾邮件过滤
"auth login\r\n",//请求login方式登陆认证
"dGVzdGFhYXd3\r\n",//用户名的base64
"cGFzc3dkMTIz\r\n",//密码的base64
"mail from:testaaaww@sina.com\r\n",//发件人，一般服务器限制与用户名对应，
"rcpt to:testaaaww@sina.com\r\n",//收件人
"data\r\n",//内容开始
"subject:title long long long\r\n"//邮件标题
"from:testaaaww@sina.com\r\n"//发件人
"to:testaaaww@sina.com\r\n"//收件人
"MIME-Version: 1.0\r\n"
"Content-Type: multipart/mixed;\r\n"
"\tboundary=\"this_is_a_unique_string\";\r\n"//定义内容边界，任意唯一字符串即可
"Content-Transfer-Encoding: 8bit\r\n"
"\r\n"
"This is a multi-part message in MIME format.\r\n"
"\r\n"
"--this_is_a_unique_string\r\n"//开始文本内容
"Content-Type: text/plain; charset=us-ascii\r\n"
"Content-Transfer-Encoding: 8bit\r\n"
"\r\n"
"this is a pure text content\r\n"
"\r\n"
"--this_is_a_unique_string\r\n"//开始附件img.jpg
"Content-Type: image/jpg;\r\n"
"\tname=\"img.jpg\";\r\n"
"Content-Transfer-Encoding: base64\r\n"
"Content-Disposition: attachment; filename=\"img.jpg\"\r\n"//它是attachment：img.jpg
"\r\n"//图片内容的base64
"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\r\n"
"\r\n"
"--this_is_a_unique_string\r\n"//内容分隔结束
".\r\n",//data内容结束
"quit\r\n",//断开链接
};
int main(int argc,char** argv)
{
FZsocket conn;
char buf[128];
int ret;
if(!conn.Open(HOST,PORT))
{
for(int i=0;i<sizeof(msg)/sizeof(msg[0]);i++)
{
ret = conn.Recv((void*)buf,sizeof(buf));
printf("%.*s\n",ret,buf);
printf("%s",msg[i]);
conn.Send((void*)msg[i],strlen(msg[i]));
}
ret = conn.Recv((void*)buf,sizeof(buf));
printf("%.*s\n",ret,buf);
conn.Shutdown();
}
return 0;
}
执行程序
[cz@myhost mail]$ ./main
220 irxd5-202.sinamail.sina.com.cn ESMTP
ehlo mailer.com
250-irxd5-202.sinamail.sina.com.cn
250-8BITMIME
250-SIZE 83886080
250-AUTH PLAIN LOGIN
250 AUTH=PLAIN LOGIN
auth login
334 VXNlcm5hbWU6
dGVzdGFhYXd3
334 UGFzc3dvcmQ6
cGFzc3dkMTIz
235 #2.0.0 OK Authenticated
mail from:testaaaww@sina.com
250 sender ok
rcpt to:testaaaww@sina.com
250 recipient ok
data
354 go ahead
subject:title long long long
from:testaaaww@sina.com
to:testaaaww@sina.com
MIME-Version: 1.0
Content-Type: multipart/mixed;
boundary=”this_is_a_unique_string”;
Content-Transfer-Encoding: 8bitThis is a multi-part message in MIME format.
–this_is_a_unique_string
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 8bitthis is a pure text content
–this_is_a_unique_string
Content-Type: image/jpg;
name=”img.jpg”;
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=”img.jpg”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
–this_is_a_unique_string
.
250 ok: Message 196395725 accepted
quit
221 irxd5-202.sinamail.sina.com.cn
收到邮件
那些其他的指令和标准在这里就不再详述，因为我想那也不是大多数人感兴趣的东西。这些就够玩的了。^-^
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