Here is a working example in Perl. Read RFC 821 for the protocol. Unless you are familiar with socket.h and socket.c I would suggest using IO::Socket::INET as it is much more intuitive to use. Note Net::SMTP is a much better option than code like this simple example which is just to show how it works.

#!/usr/bin/perl -w

use strict;
use IO::Socket::INET;

# see RFC 821 http://www.ietf.org/rfc/rfc0821.txt

my $forged_from = 'hotmail.com';
my $from        = 'nobody@hotmail.com';
my $to          = 'smtp_test@hotmail.com';
my $msg         = "Subject: Subject\n\nHello me!\n\nNew Line\nMore Lin
+es\n";
my $server      = 'xxxx.xxxx.net.au';  # SMTP SERVER
my $port        = 25;
my $timeout     = 10;

my $sock = IO::Socket::INET->new( PeerAddr => $server,
                                  PeerPort => $port,
                                  Proto    => 'tcp',
                                  Timeout  => $timeout,     
);
unless ( $sock ) {
  die"ERR - Could not connect socket to $server on port $port";
}

if ( my $server = <$sock>) {
    print "Got Handshake: $server";
    dialog( $sock,  "HELO $forged_from\015\012" );
    dialog( $sock,  "MAIL FROM: $from\015\012" );
    dialog( $sock,  "RCPT TO: $to\015\012" );
    dialog( $sock,  "DATA\015\012" );
    dialog( $sock,  "$msg\015\012.\015\012" );
    dialog( $sock,  "QUIT\015\012" );
}
else {
    die "No handshake sent from SMTP server\n"
}


sub dialog {
    my ( $sock, $send ) = @_;
    print $sock $send;
    print "Sent: $send";
    my $receive = <$sock>;
  die "Got no response to $send" unless $receive;
    print "Recv: $receive";
}

__DATA__
Got Handshake: 220 xxxx.xxxx.net.au ESMTP Sendmail 8.11.6/8.11.6; Sat,
+ 20 Dec 2003 21:39:21 +1100 (EST)

Sent: HELO hotmail.com

Recv: 250 xxxx.xxxx.net.au Hello blah.blah.blah.blah.com.au [203.220.x
+xx.xxx], pleased to meet you

Sent: MAIL FROM: nobody@hotmail.com

Recv: 250 2.1.0 nobody@hotmail.com... Sender ok

Sent: RCPT TO: smtp_test@hotmail.com

Recv: 250 2.1.5 smtp_test@hotmail.com... Recipient ok

Sent: DATA

Recv: 354 Please start mail input.

Sent: Subject: Subject

Hello me!

New Line
More Lines


.

Recv: 250 Mail queued for delivery.

Sent: QUIT

Recv: 221 Closing connection. Good bye.
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