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.
[download]

I think the answers to some of your questions are:

1. $mailserver will be the mailserver you will be sending thru, such as smtp.yourdomain.com or something.
2. TCP is the underlying protocol used for the data transmission (as opposed to UDP or ICMP), whereas SMTP is the application protocol.

I *believe* (but am not for 100% sure) that $serverAddr is the address of the server you will be connecting to. As to the pack format, this may be of help. In the code, it appears as if it is being used in the initial connection (although I am not certain).

Hope that helps (a little, at least).

1. If you want to really learn about network programming in Perl, get Network Programming with Perl and read/program away. It's worth every penny.
2. If you just want to send an email, or more importantly, you are seriously going to need to plug email submissions in your CGI app, then use MIME::Lite. It's as easy as: (straight from the docs)

   my $msg = MIME::Lite->new(
      From     =>'me@myhost.com',
      To       =>'you@yourhost.com',
      Cc       =>'some@other.com, some@more.com',
      Subject  =>'Helloooooo, nurse!',
      Data     =>"How's it goin', eh?"
   );
   $msg->send;
   [download]

   Really. Raw socket programming is worth learning, but after you do learn how to unclog the pipes to your toliet, do you really want to keep Doing It The Hard Way? ;)

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

I don't think that any direct answer would actually help you much, as I can see you are really new to network communication. No Perl book can clearly help you on this, and I strongly suggest you to read some books about network, its layered architecture, and its main protocols in general.

Learning takes time, don't rush, try to make the foundation solid.