C语言发送邮件 基于libesmtp库

其他方法：（基于libesmtp库）

1、安装库libesmtp-devel

yum install libesmtp-devel
或
apt-get install libesmtp-devel

如果没法用命令安装，就上http://www.stafford.uklinux.net/libesmtp/自己下载包安装。

2、不认证即可发信息

#define _XOPEN_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <getopt.h>
#include <string.h>
#include <fcntl.h>
#include <signal.h>
#include <errno.h>
#include <stdarg.h>
#include <libesmtp.h>

int main() {
    smtp_session_t session;
    smtp_message_t message;
    struct sigaction sa;
    const smtp_status_t *status;
    char buf[128];
    FILE *fp;
    /* This program sends only one message at a time. Create an SMTP
       session and add a message to it. */
    if( (session = smtp_create_session ()) == NULL){
        fprintf (stderr, "smtp_create_session problem %s\n",
                smtp_strerror (smtp_errno (), buf, sizeof buf));
        return 1;
    }
    if((message = smtp_add_message (session)) == NULL){
        fprintf (stderr, "smtp_add_message problem %s\n",
                smtp_strerror (smtp_errno (), buf, sizeof buf));
        return 1;
    }
    /* NB. libESMTP sets timeouts as it progresses through the protocol.
       In addition the remote server might close its socket on a timeout.
       Consequently libESMTP may sometimes try to write to a socket with
       no reader. Ignore SIGPIPE, then the program doesn't get killed
       if/when this happens. */
    sa.sa_handler = SIG_IGN;
    sigemptyset (&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction (SIGPIPE, &sa, NULL); 
    /* Set the host running the SMTP server. LibESMTP has a default port
       number of 587, however this is not widely deployed so the port
       is specified as 25 along with the default MTA host. */
    smtp_set_server (session, "127.0.0.1:25");
    /* Set the reverse path for the mail envelope. (NULL is ok)
     */
    smtp_set_reverse_path (message, "[e-mail]");
    /* RFC 2822 doesn't require recipient headers but a To: header would
     * be nice to have if not present. */
    smtp_set_header (message, "To", NULL, NULL);
    smtp_set_header (message, "Subject", " test mail");
    smtp_set_header_option (message, "Subject", Hdr_OVERRIDE, 1);
    fprintf(stderr,"%s\n","smtp_set_server.");
    if ((fp = fopen ("test-mail.eml", "r")) == NULL) {
        fprintf (stderr, "can't open mail file: %s\n", strerror (errno));
        return (1);
    }
    smtp_set_message_fp (message, fp);
    smtp_add_recipient (message,"[e-mail]");
    /* Initiate a connection to the SMTP server and transfer the
       message. */
    if (!smtp_start_session (session)){
        fprintf (stderr, "SMTP server problem %s\n",
                smtp_strerror (smtp_errno (), buf, sizeof buf));
    }
    else{
        /* Report on the success or otherwise of the mail transfer.
        */
        status = smtp_message_transfer_status (message);
        printf ("%d %s", status->code,
                (status->text != NULL) ? status->text : "\n");
    }
    /* Free resources consumed by the program.
    */
    smtp_destroy_session (session);
    if(fp != NULL){
        fclose(fp);
    }

    return 0;
}

3、把上面的代码写入sendmail.c，并把里面的"[e-mail]"替换成你自己的QQ邮箱地址或者其它邮箱地址，然后用下面命令编译

gcc -std=c99 -Wall `libesmtp-config --cflags`   -o sendmail sendmail.c -lesmtp

4、同目录下新建test-mail.eml文件，里面内容随便自己填。

5、运行

./sendmail