/***********************************************/
/* SMTPTest.cpp                                */
/* A program to test SMTP mail communications  */
/*                                             */
/* Compile with:                               */
/* cl SPAMSend.c /link ws2_32.lib advapi32.lib */
/*                                             */
/***********************************************/
#include <stdio.h>
#include <winsock.h>
 
/*****************/
/* MAIN FUNCTION */
/*****************/
void main(int nArgc, char *pArgv[] )
{
	WSADATA				wsaData;
	SOCKET				s;				/* Socket identifier */
 
	char				buf[255];		/* Buffer for incoming */
	int					n;				/* Bytes to read */
	struct servent		*ServEntry;		/* Pointer to service info entry */
	struct hostent		*HostEntry;
	struct sockaddr_in	sin;			/* Internet socket structure */
	int					type;			/* socket type */
 
    // Evaluate arguments
    printf("SMTPTest v1.0\n\n");
    if ( nArgc != 2 )
    {
        printf("  A program to test SMTP mail communications.\n");
        printf("\nUsage:\t%s mailsystem\n\n", strupr(pArgv[0]));
        printf("\tmailsystem = IP address or DNS name of mail forwarder\n");
        return;
    }
 
    // Initialize WinSock
    if (WSAStartup( MAKEWORD( 2, 0), &wsaData) != 0)
    {
        printf("ERROR: Error starting up WinSock\n");
        return;
    }
 
    // Allocate a socket
    s = socket(PF_INET, SOCK_STREAM, 0);
    if ( s == INVALID_SOCKET )
    {
        printf("ERROR: Invalid socket\n");
        WSACleanup();
        return;
    }
 
    memset(&sin, 0, sizeof(sin));		    // Clear out all variables in socket structure
    sin.sin_family = AF_INET;			    // Set protocol to IP
 
    // Set port to SMTP
    if (ServEntry = getservbyname("smtp", "tcp"))
    {
        sin.sin_port = ServEntry->s_port;
    }
    else
    {
        printf("ERROR: Port discovery error\n");
        WSACleanup();
        return;
    }
 
    // Perform DNS resolution of IP address of mail server
	if ( (sin.sin_addr.s_addr = inet_addr(pArgv[1])) == INADDR_NONE)
	{
		if ( HostEntry = gethostbyname(pArgv[1]) )
		{
			memcpy(&sin.sin_addr, HostEntry->h_addr, HostEntry->h_length);
		}
		else
		{
			printf("ERROR: Can't get \"%s\" host entry\n", pArgv[1]);
			WSACleanup();
			return;
		}
	}
	printf("%s resolves to %s\n", pArgv[1], inet_ntoa(sin.sin_addr));
 
    // Connect a TCP socket to the server
    if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) == SOCKET_ERROR)
    {
        printf("ERROR: Cannot connect to server\n");
        WSACleanup();
        return;
    }
 
    // Receive mail server header
	buf[0] = '\0';
    n = recv(s, buf, 255, 0);
    if ( n == SOCKET_ERROR )
    {
		printf("ERROR: Cannot receive data\n");
		goto Cleanup;
	}
    buf[n-1] = '\0';
    printf("RECV> %s\n", buf);
 
    // Send "helo" to the server
    sprintf(buf, "helo company.com\r\n");
    n = send(s, buf, strlen(buf), 0);
 
    if ( n == SOCKET_ERROR )
    {
		printf("ERROR: Cannot send data\n");
		goto Cleanup;
	}
	buf[strlen(buf)-1] = '\0';
    printf("SEND> %s\n", buf);
 
    // Receive "250 OK" response from server
	buf[0] = '\0';
    n = recv(s, buf, 255, 0);
    if ( n == SOCKET_ERROR )
    {
		printf("ERROR: Cannot receive data\n");
		goto Cleanup;
	}
    buf[n-1] = '\0';
    printf("RECV> %s\n", buf);
 
    // Send "Quit" to the server
	sprintf(buf, "quit\r\n");
    n = send(s, buf, strlen(buf), 0);
    if ( n == SOCKET_ERROR )
    {
		printf("ERROR: Cannot send data\n");
		goto Cleanup;
	}
	buf[strlen(buf)-1] = '\0';
    printf("SEND> %s\n", buf);
 
    // Receive "221 closing connection" from the server
    n = recv(s, buf, 255, 0);
    if ( n == SOCKET_ERROR )
    {
		printf("ERROR: Cannot receive data\n");
		goto Cleanup;
	}
    buf[n-1] = '\0';
    printf("RECV> %s\n", buf);
 
    // Close TCP socket
Cleanup:
    if (shutdown(s, 0) != 0)
    {
        printf("Error with shutdown\n");
        WSACleanup();
        return;
    }
 
    // Cleanup WinSock
    if ( WSACleanup() != 0 )
    {
        printf("Error shutting down WinSock\n");
        return;
    }
 
    return;
}

C:\Source\Work\SMTPTest>smtptest 192.168.1.104
SMTPTest v1.0
 
192.168.1.104 resolves to 192.168.1.104
Connected: 0
RECV>
SEND> helo company.com
RECV>
SEND> quit
ERROR: Cannot receive data
 
C:\Source\Work\SMTPTest>

	printf("Connected: %u\n", WSAGetLastError());