According to the docs for Net::SMTP,

Unless otherwise stated all methods return either a *true* or *false* value, with *true* meaning that the operation was a success. When a method states that it returns a value, failure will be returned as *undef* or an empty list.

So, you should simply check the return value of $smtp->dataend().

my $smtp = Net::SMTP->new('smtp.orcon.net.nz',
                           Timeout => 30,
                           Debug   => 0,  # Prevent debug info to STDO
+UT
                          );


$smtp->mail('no@one.com'); # Don't need to escape @ in single-quotes
$smtp->to('xxx@yyy.com');  # Fixed typo; you forgot opening quote. :)
$smtp->data();
$smtp->datasend("To: xxx\@yyy.com\n");
$smtp->datasend("\n");
$smtp->datasend("A simple test message\n");
my $res = $smtp->dataend();
$smtp->quit;

print "Operation was ", $res ? '' : 'un', "successful.\n";
[download]

Also, you might want to just pass the message to $smtp->data(), as it looks cleaner (personal opinion :)

use Net::SMTP;

my $smtp = Net::SMTP->new('smtp.example.com',
                           Timeout => 30,
                           Debug   => 0,  # Prevent debug info to STDO
+UT
                          );


$smtp->mail('someone@example.com');
$smtp->to('someone@example.com');
my $ret = $smtp->data(<<'EOM');
From: someone@example.com
To: someone@example.com
Subject: Test Message

A simple test message.
EOM

print "Operation was ", $ret ? '' : 'un', "successfull.\n";
print "(Got response: ", $smtp->message(), ")\n";

$smtp->quit;
[download]

bbfu
Black flowers blossum
Fearless on my breath

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