使用telnet发送邮件

通过使用cmd下的telnet发送一封邮件，掌握SMTP发送邮件的过程。

1. 准备工作

对发送方邮箱地址进行base64编码。
对发送方邮箱授权码进行base64编码。

Python进行base64编码方法：

>>> import base64
>>> base64.b64encode(b"123456@163.com") # b表示使用ascii对字符串进行编码
b'MTIzNDU2QDE2My5jb20='

2. 发送邮件

打开cmd
输入telnet smtp.163.com 25

进入telnet后，依次输入以下内容

helo 163.com # 打招呼
auth login # 登录命令
MTIzNDU2QDE2My5jb20= # base64编码后的发送方邮箱地址
MTIzNDU2 # base64编码后的发送方邮箱授权码
mail from: <vfyouv655@163.com> # 注明发件人
rcpt to: <963312591@qq.com> # 注明收件人
data # 表示接下来开始输入数据部分
from:vfyouv655@163.com # 注明发件人
to:963312591@qq.com # 注明收件人
subject:Test # 输入邮件主题
             # 一个空行
i am testing to send mail # 邮件正文
             # 一个空行
. # 表示邮件内容输入结束

正常情况结果如下图所示

使用QT实现以上内容

记得在.pro文件中引入network模块。下面直接上代码。

widget.h文件内容

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QTcpSocket>
#include <QAbstractSocket>
#include <QMessageBox>
#include <QDebug>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = nullptr);
    ~Widget();

private slots:
    void readyReadSlot();

private:
    //检查连接状态
    void checkConnectState();
    //发送helo
    void sendHelo();
    //发送auth login
    void sendAuthLogin();
    //发送用户名
    void sendUser();
    //发送密码
    void sendPassword();
    //发送mail from
    void sendMailFrom();
    //发送rcpt to
    void sendRcptTo();
    //发送data
    void sendData();
    //发送邮件内容
    void sendContent();
    //发送成功后续操作
    void afterSendSuccess();

private:
    Ui::Widget *ui;

    QString senderMail; //发送方邮箱地址
    QString authCode; //发送方邮箱授权码
    QString receiveMail; //接收方邮箱地址

    QString title; //邮件标题
    QString content; //邮件正文

    QString expectedReply; //期待收到的应答
    void (Widget::*nextAction)(); //收到正确应答后下一步要执行的方法

    QTcpSocket *tcpSocket;
};

#endif // WIDGET_H

widget.cpp文件内容

#pragma execution_character_set("utf-8")
#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget),
    senderMail("这里填写发送方邮箱地址"), authCode("这里填写发送方邮箱授权码"), receiveMail("这里填写接收方邮箱地址"),
    expectedReply("220 163.com Anti-spam GT for Coremail System"), nextAction(&Widget::checkConnectState)
{
    ui->setupUi(this);

    //设置邮件的标题和正文
    this->title = "这是邮件标题";
    this->content = "这句话是邮件的正文";

    //tcpSocket初始化
    this->tcpSocket = new QTcpSocket(this);
    tcpSocket->connectToHost("smtp.163.com", 25);
    connect(tcpSocket, &QTcpSocket::readyRead,this, &Widget::readyReadSlot);
}

Widget::~Widget()
{
    delete ui;
}

void Widget::readyReadSlot()
{
    QByteArray buffer = tcpSocket->readAll();
    qDebug()<<"收到服务器回复："<<buffer;

    if(buffer.contains(this->expectedReply.toLatin1())){
        if(nextAction) (this->*nextAction)();
    }
    else{
        QMessageBox::warning(this, "提示", "邮件发送失败!");
    }
}

//检查连接状态
void Widget::checkConnectState()
{
    if(tcpSocket->state() == QAbstractSocket::ConnectedState){
        sendHelo();
    }
    else{
        QMessageBox::warning(this, "提示", "连接失败！");
    }
}

//发送helo
void Widget::sendHelo()
{
    QString str = "helo 163.com\r\n";
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toLatin1());
    this->expectedReply = "250 OK\r\n";
    this->nextAction = &Widget::sendAuthLogin;
}

//发送auth login
void Widget::sendAuthLogin()
{
    QString str = "auth login\r\n";
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toLatin1());
    this->expectedReply = "334 dXNlcm5hbWU6\r\n";
    this->nextAction = &Widget::sendUser;
}

//发送用户名
void Widget::sendUser()
{
    QString str = QString("\r\n").prepend(senderMail.toLatin1().toBase64());
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toLatin1());
    this->expectedReply = "334 UGFzc3dvcmQ6\r\n";
    this->nextAction = &Widget::sendPassword;
}

//发送密码
void Widget::sendPassword()
{
    QString str = QString("\r\n").prepend(authCode.toLatin1().toBase64());
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toLatin1());
    this->expectedReply = "235 Authentication successful\r\n";
    this->nextAction = &Widget::sendMailFrom;
}

//发送mail from
void Widget::sendMailFrom()
{
    QString str = QString("mail from: <%1>\r\n").arg(senderMail);
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toLatin1());
    this->expectedReply = "250 Mail OK\r\n";
    this->nextAction = &Widget::sendRcptTo;
}

//发送rcpt to
void Widget::sendRcptTo()
{
    QString str = QString("rcpt to: <%1>\r\n").arg(receiveMail);
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toLatin1());
    this->expectedReply = "250 Mail OK\r\n";
    this->nextAction = &Widget::sendData;
}

//发送data
void Widget::sendData()
{
    QString str = "data\r\n";
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toLatin1());
    this->expectedReply = "354 End data with <CR><LF>.<CR><LF>\r\n";
    this->nextAction = &Widget::sendContent;
}

//发送邮件内容
void Widget::sendContent()
{
    QString str = QString("from:%1\r\n"
                          "to:%2\r\n"
                          "subject:=?UTF-8?B?%3?=\r\n"
                          "\r\n"
                          "%4\r\n"
                          "\r\n"
                          ".\r\n").arg(senderMail).arg(receiveMail).arg( QString("").append(title.toUtf8().toBase64()) ).arg(content);
    qDebug()<<"向服务器发送：　" + str;
    tcpSocket->write(str.toUtf8());
    this->expectedReply = "250 Mail OK queued as";
    this->nextAction = &Widget::afterSendSuccess;
}

//发送成功后续操作
void Widget::afterSendSuccess()
{
    QMessageBox::information(this, "提示", "邮件发送成功!");
}