您可以直接使用本地MTA popen()并向其提供符合RFC822的文本。

#include <stdio.h>
#include <string.h>
#include <errno.h>
int sendmail(const char *to, const char *from, const char *subject, const char *message)
{
    int retval = -1;
    FILE *mailpipe = popen("/usr/lib/sendmail -t", "w");
    if (mailpipe != NULL) {
        fprintf(mailpipe, "To: %s\n", to);
        fprintf(mailpipe, "From: %s\n", from);
        fprintf(mailpipe, "Subject: %s\n\n", subject);
        fwrite(message, 1, strlen(message), mailpipe);
        fwrite(".\n", 1, 2, mailpipe);
        pclose(mailpipe);
        retval = 0;
     }
     else {
         perror("Failed to invoke sendmail");
     }
     return retval;
}

main(int argc, char** argv)
{
    int i;

    printf("argc = %d\n", argc);

    for (i = 0; i < argc; i++)
        printf("argv[%d] = \"%s\"\n", i, argv[i]);
    sendmail(argv[1], argv[2], argv[3], argv[4]);
}