#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <stdio.h>
#include <string.h>
#include <unistd.h>

int my_socket;

void snd(char *s)
{
send(my_socket, s, strlen(s), 0);
}

int printUsage(char *progname)
{
printf("Usage: %s -t destination [-f from] [-s subject] -m message\n", progname);
return 1;
}

int main(int argc, char *argv[])
{
int ret;
struct sockaddr_in my_addr;

char *from=0, *to=0, *subject=0, *message=0;
bool verbose = false;
char optchar;
while ((optchar = getopt (argc, argv, "f:t:s:m:v")) != -1)
{
switch (optchar)
{
case 'f':
from = strdup(optarg);
break;
case 't':
to = strdup(optarg);
break;
case 's':
subject = strdup(optarg);
break;
case 'm':
message = strdup(optarg);
break;
case 'v':
verbose = true;
break;
default:
return printUsage(argv[0]);
}
}

if(!to || !message)
return printUsage(argv[0]);

if(!subject)
subject = strdup("No subject");

if(!from)
from = strdup("Unknown");

if(verbose)
{
printf("From: %s\n", from);
printf("To: %s\n", to);
printf("Subject: %s\n", subject);
printf("Message: %s\n", message);
}


my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(25);
my_addr.sin_addr.s_addr = inet_addr("24.201.245.36");
memset(&(my_addr.sin_zero), '\0', 8);

my_socket = socket(AF_INET, SOCK_STREAM, 0);
if(my_socket == -1)
printf("error while initialising socket\n");

ret = connect(my_socket, (const struct sockaddr *)&my_addr, sizeof(my_addr));
if(ret == -1)
printf("unable to connect\n");


int stage = 0;
char buffer[4096];
while(1)
{
ret = recv(my_socket, buffer, 4096, 0);
if(ret != -1 && ret != 0)
{
buffer[ret] = '\0';
if(strstr(buffer, "220") == buffer)
{
if(verbose)
printf("Connected\n");
snd("HELO localhost\r\n");
}

if(strstr(buffer, "250") == buffer)
{
switch(stage)
{
case 0:
sprintf(buffer, "MAIL FROM: %s\r\n", from);
snd(buffer);
stage++;
break;
case 1:
sprintf(buffer, "RCPT TO: %s\r\n", to);
snd(buffer);
stage++;
break;
case 2:
snd("data\r\n");
stage++;
break;
case 3:
if(verbose)
printf("Closing connection\n");
snd("quit\r\n");
stage++;
break;
}
}

if(strstr(buffer, "354") == buffer)
{
if(verbose)
printf("Sending message...");
if(subject)
{
sprintf(buffer, "Subject: %s\r\n", subject);
snd(buffer);
}
snd(message);
snd("\r\n.\r\n");
if(verbose)
printf("Ok.\n");
}
}
else
break;
}

return 0;
}

            SmtpClient client = new SmtpClient("serveur smtp");// smtp.free.
           
            MailAddress from = new MailAddress("ton_mail@mail.com");

            MailAddress to = new MailAddress("mail_destinataire@gmail.com");
            
            MailMessage message = new MailMessage(from, to);
            
            message.Body = "Le corps du message";
            
            message.Subject = "le sujet";

            client.Send(message);

SmtpClient client = new SmtpClient("serveur smtp");// smtp.free.
client.Send("ton_mail@mail.com", "maildestinataire@mail.com", "sujet", "message");