create module structure

mkdir -p /etc/puppet/modules/nullmailer/manifests
mkdir -p /etc/puppet/modules/nullmailer/files

download module definiction
<?php
$URL="https://raw.githubusercontent.com/panticz/puppet/master/modules/nullmailer/init.pp";

echo "wget -q $URL -O /etc/puppet/modules/nullmailer/manifests/init.pp";
echo "<div><pre>";
</pre></div>

$c = curl_init();
curl_setopt($c, CURLOPT_URL, $URL);
curl_setopt($c, CURLOPT_RETURNTRANSFER, 1);

echo htmlspecialchars(curl_exec($c));

curl_close($c);

echo "";

?>

add include to your client in /etc/puppet/manifests/site.pp
node "client1.local" inherits default {
...
include nullmailer
...
}

Example: /etc/mailname
example.com

Example: /etc/nullmailer/remotes
smtp.example.com smtp --auth-login --user=YOUR_SMTP_ID --pass=YOUR_SMTP_PASS

Links
http://www.panticz.de/install-nullmailer