If your providers server listens on port 465 (as indicated in the code snippet above), it almost certainly expects an SSL connection (465 is the universally accepted port for SMTPS,i.e. SMTP over SSL). AFAIK you can't use SSL in conjunction with the MIME::Lite send() method (or rather, you probably could but it's more trouble than it is worth), so you'll need to use something like Net::SMTP::SSL for sending. You can still use MIME::Lite for constructing the message. For example (untested):

#!/usr/bin/perl

use strict; 
use warnings; 
use MIME::Lite::TT::HTML; 
use Net::SMTP::SSL;

my %params;
my %options; 
$options{INCLUDE_PATH} = 'c:/Documents and Settings/Uriel/My Documents
+/Sandbox/perl/'; 

my $msg = MIME::Lite::TT::HTML->new( 
            From        =>  'admin@example.com',
            To          =>  'test@yahoo.com', 
            Subject     =>  'Hello world', 
            Template    =>  {
                                text    =>  'test.txt',
                                html    =>  'test.html',
                            },
            TmplOptions =>  \%options, 
            TmplParams  =>  \%params, 
); 

my $smtp; 
$smtp = Net::SMTP::SSL->new($host, Port=>465) or die "Can't connect";
$smtp->auth($user, $pass) or die "Can't authenticate:".$smtp->message(
+);
$smtp->mail('admin@example.com') or die "Error:".$smtp->message();
$smtp->to('test@yahoo.com') or die "Error:".$smtp->message();
$smtp->data() or die "Error:".$smtp->message();
$smtp->datasend($msg->as_string) or die "Error:".$smtp->message();
$smtp->dataend() or die "Error:".$smtp->message();
$smtp->quit() or die "Error:".$smtp->message();
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