Thread: SMTP prolem

Hi!

I went through an emailing tutorial, and ended up with the code below. But it doesn’t work. I get no compiler errors/warnings, nor runtime errors. Though it doesn’t send the email. Could someone please checkout the code and see what’s wrong?
Thanks a lot.

Code:

	struct sockaddr_in A;WSADATA W;SOCKET S;struct hostent *H;
	char aa[100];int i;char R[10000];
	
	WSAStartup (0x101, &W);
	
	S=socket(AF_INET, SOCK_STREAM,0);
	
	A.sin_family=AF_INET;
	A.sin_port = htons(25); // SMPT is on port 25
	H=gethostbyname("yahoo.com"); // get info on the email server
	cout<<"gethostbyname()"<<GetLastError()<<endl;
	A.sin_addr.s_addr=*((unsigned long *) H->h_addr); // convert the SMTP sites address into a IPA and store
	i=connect(S,(struct sockaddr *) &A,sizeof(A)); // connect to the server
	cout<<"connect()"<<GetLastError()<<endl;
	
	i=recv(S,R,10000,0); // wait until the connection establishes
	cout<<"recv()[connect]"<<GetLastError()<<endl;
	strset(aa,' ');
	strcpy(R,"HELO P2V2E0\r\n");  // 1st command . computer name

	i=send(S,R,strlen(R),0);
	cout<<"send()"<<GetLastError()<<endl;
	
	i=recv(S,R,10000,0);
	cout<<"recv()[send]"<<GetLastError()<<endl;
	strset(aa,' ');
	
	strcpy(R,"MAIL FROM:<[email protected]>\r\n"); // our address
	i=send(S,R,strlen(R),0);
	
	i=recv(S,R,10000,0);
	strset(aa,' ');
	
	strcpy(R,"RCPT  TO:<[email protected]>\r\n"); // recepients' address
	i=send(S,R,strlen(R),0);
	
	i=recv(S,R,10000,0);
	strset(aa,' ');
	
	strcpy(R,"DATA\r\n"); // email begins
	i=send(S,R,strlen(R),0);
	
	i=recv(S,R,10000,0);
	strset(aa,' ');  
	
	strcpy(R,"TO: [email protected]\r\n");
	//strcpy(R,"TO: aaa.com\r\n");
	i=send(S,R,strlen(R),0);
	
	strcpy(R,"FROM: [email protected]\r\n");
	i=send(S,R,strlen(R),0);
	
	strcpy(R,"DATE: 27 April 05 3:05 PST\r\n");
	i=send(S,R,strlen(R),0);
	
	strcpy(R,"MESSAGE_ID: <[email protected]>\r\n");
	i=send(S,R,strlen(R),0);
	
	strcpy(R,"Hello\r\n");
	i=send(S,R,strlen(R),0);
	
	strcpy(R,"How are you\r\n");
	i=send(S,R,strlen(R),0);
	
	strcpy(R,".\r\n"); // end the mail with a period
	i=send(S,R,strlen(R),0);
	
	i=recv(S,R,10000,0);
	strset(aa,' ');
	
	strcpy(R,"QUIT\r\n"); // end mail
	i=send(S,R,strlen(R),0);
	
	i=recv(S,R,10000,0);

Try this instead:

Code:

struct sockaddr_in A;
struct hostent *H;

if((h = gethostbyname("yahoo.com")) == NULL)
  return;
A.sin_addr = *(struct in_addr*)H->h_addr_list[0];
A.sin_port = htons(usPort);
A.sin_family = AF_INET;

S=socket(AF_INET, SOCK_STREAM, 0);
connect, etc.....

gethostbyname will return the A records for a domain. To find the mail server for a domain you must request the MX records. This will return zero or more mail server domains (you should use the one with the lowest preference). You can then use gethostbyname to retrieve the IP address for the mail server (this is often included in the original response as a matter of efficiency). Winsock does not provide MX lookup functionality. However, Windows 2000 and above include a DNS API. Alternatively, there is code on the web that implements a DNS client. For temporary testing, you can use a web page to look up the MX servers.

Sample code that uses the Windows DNS API to query the MX records for yahoo.com:

Code:

#include <windows.h>
#include <windns.h>
#include <stdio.h>

#if defined(_MSC_VER)
#pragma comment(lib, "dnsapi.lib")
#endif

char* SectionToString(DWORD section)
{
	switch (section)
	{
		case DNSREC_QUESTION:   return "Question";
		case DNSREC_ANSWER:     return "Answer";
		case DNSREC_AUTHORITY:  return "Authority";
		case DNSREC_ADDITIONAL: return "Additional";
	}

	return "Unknown";
}

int main(void)
{
	DNS_RECORD* pRecordList = NULL;
	DNS_RECORD* pRecord     = NULL;

	/* Send the DNS query... */
	DnsQuery_A("yahoo.com", DNS_TYPE_MX, DNS_QUERY_STANDARD, NULL, &pRecordList, NULL);

	/* Walk through the linked list of DNS records... */
	for (pRecord = pRecordList; pRecord != NULL; pRecord = pRecord->pNext)
	{
		printf("\nSection:      %s\n", SectionToString(pRecord->Flags.S.Section));
		printf(  "Domain Name:  %s\n", (char*) pRecord->pName);
		printf(  "Record Type:  %d\n",         pRecord->wType);
		printf(  "Time-To-Live: %d\n",         pRecord->dwTtl);

		if (pRecord->wType == DNS_TYPE_MX)
		{
			printf("  MX Server:  %s\n", (char*) pRecord->Data.MX.pNameExchange);
			printf("  Preference: %d\n",         pRecord->Data.MX.wPreference);
		}
	}

	DnsRecordListFree(pRecordList, DnsFreeRecordList);

	getchar();
	return 0;
}

Output:

Code:

// Answer records contain the MX servers for yahoo.com
Section:      Answer
Domain Name:  yahoo.com
Record Type:  15
Time-To-Live: 770
  MX Server:  mx4.mail.yahoo.com
  Preference: 5

Section:      Answer
Domain Name:  yahoo.com
Record Type:  15
Time-To-Live: 770
  MX Server:  mx1.mail.yahoo.com
  Preference: 1

Section:      Answer
Domain Name:  yahoo.com
Record Type:  15
Time-To-Live: 770
  MX Server:  mx2.mail.yahoo.com
  Preference: 1

Section:      Answer
Domain Name:  yahoo.com
Record Type:  15
Time-To-Live: 770
  MX Server:  mx3.mail.yahoo.com
  Preference: 1

// These additional records contain the IP addresses for
// the MX servers. This saves an extra lookup.
Section:      Additional
Domain Name:  mx1.mail.yahoo.com
Record Type:  1
Time-To-Live: 770

Section:      Additional
Domain Name:  mx2.mail.yahoo.com
Record Type:  1
Time-To-Live: 770

...

// These additional records contain the IP addresses for the yahoo
// name server.
Section:      Additional
Domain Name:  ns1.yahoo.com
Record Type:  1
Time-To-Live: 770

Section:      Additional
Domain Name:  ns2.yahoo.com
Record Type:  1
Time-To-Live: 770

...