使用C发送电子邮件

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define SMTP_SERVER "smtp.example.com"
#define SMTP_PORT 25

int main() {
    int sock;
    struct sockaddr_in server;
    char message[1024], server_reply[4096];

    // 创建socket
    sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == -1) {
        printf("Failed to create socket\n");
        return 1;
    }

    server.sin_addr.s_addr = inet_addr(SMTP_SERVER);
    server.sin_family = AF_INET;
    server.sin_port = htons(SMTP_PORT);

    // 连接到SMTP服务器
    if (connect(sock, (struct sockaddr *)&server, sizeof(server)) < 0) {
        printf("Failed to connect to SMTP server\n");
        return 1;
    }

    // 接收服务器的欢迎消息
    if (recv(sock, server_reply, sizeof(server_reply), 0) < 0) {
        printf("Failed to receive server reply\n");
        return 1;
    }

    printf("Server reply: %s\n", server_reply);

    // 发送HELO命令
    strcpy(message, "HELO example.com\r\n");
    if (send(sock, message, strlen(message), 0) < 0) {
        printf("Failed to send HELO command\n");
        return 1;
    }

    // 接收服务器的回复
    if (recv(sock, server_reply, sizeof(server_reply), 0) < 0) {
        printf("Failed to receive server reply\n");
        return 1;
    }

    printf("Server reply: %s\n", server_reply);

    // 发送MAIL FROM命令
    strcpy(message, "MAIL FROM: <sender@example.com>\r\n");
    if (send(sock, message, strlen(message), 0) < 0) {
        printf("Failed to send MAIL FROM command\n");
        return 1;
    }

    // 接收服务器的回复
    if (recv(sock, server_reply, sizeof(server_reply), 0) < 0) {
        printf("Failed to receive server reply\n");
        return 1;
    }

    printf("Server reply: %s\n", server_reply);

    // 发送RCPT TO命令
    strcpy(message, "RCPT TO: <recipient@example.com>\r\n");
    if (send(sock, message, strlen(message), 0) < 0) {
        printf("Failed to send RCPT TO command\n");
        return 1;
    }

    // 接收服务器的回复
    if (recv(sock, server_reply, sizeof(server_reply), 0) < 0) {
        printf("Failed to receive server reply\n");
        return 1;
    }

    printf("Server reply: %s\n", server_reply);

    // 发送DATA命令
    strcpy(message, "DATA\r\n");
    if (send(sock, message, strlen(message), 0) < 0) {
        printf("Failed to send DATA command\n");
        return 1;
    }

    // 接收服务器的回复
    if (recv(sock, server_reply, sizeof(server_reply), 0) < 0) {
        printf("Failed to receive server reply\n");
        return 1;
    }

    printf("Server reply: %s\n", server_reply);

    // 发送邮件内容
    strcpy(message, "Subject: Test Email\r\n");
    strcat(message, "From: sender@example.com\r\n");
    strcat(message, "To: recipient@example.com\r\n");
    strcat(message, "\r\n");
    strcat(message, "This is a test email.\r\n");
    strcat(message, ".\r\n");
    if (send(sock, message, strlen(message), 0) < 0) {
        printf("Failed to send email content\n");
        return 1;
    }

    // 接收服务器的回复
    if (recv(sock, server_reply, sizeof(server_reply), 0) < 0) {
        printf("Failed to receive server reply\n");
        return 1;
    }

    printf("Server reply: %s\n", server_reply);

    // 发送QUIT命令
    strcpy(message, "QUIT\r\n");
    if (send(sock, message, strlen(message), 0) < 0) {
        printf("Failed to send QUIT command\n");
        return 1;
    }

    // 接收服务器的回复
    if (recv(sock, server_reply, sizeof(server_reply), 0) < 0) {
        printf("Failed to receive server reply\n");
        return 1;
    }

    printf("Server reply: %s\n", server_reply);

    // 关闭socket
    close(sock);

    return 0;
}