Here's a corrected version that works under -w and strict:

use strict;

use Mail::Mailer;

my $from_address = "perlmonk";
my $to_address = "user\@localhost";
my $subject = "hi";
my $body = "hello";

my $mailer = Mail::Mailer->new("sendmail");
$mailer->open({ 
    From    => $from_address,
    To      => $to_address,
    Subject => $subject,
}); 
print $mailer $body;
$mailer->close();
[download]

(note that there was a missing semicolon)

and the second:

open(MAIL, "|/usr/lib/sendmail -oi -t -odq") || die "Can't open sendma
+il: $!";
print MAIL <<MESSAGE;
From: Your name <emailaddress\@blah.com>
To: Recipient name <email address\@blah2.com>
Subject: Mailing with Perl

this is easy.
MESSAGE
close(MAIL);
[download]

(note that the heredoc was broken)