Ejemplos de API con archivos adjuntos

<?php
require_once 'HTTP/Request2.php';

$config = array('use_brackets' => false,
               );

$request = new HTTP_Request2('https://rsXXX-api.realsender.com/mail/send',
                             HTTP_Request2::METHOD_POST,
                             $config);

$data = array('apiuser' => 'the one we provided you',
              'apipass' => 'the one we provided you',
              'from' => 'sender@example.com',
              'to' => 'recipient@example.com',
              'subject' => 'subject of the message',
              'text' => 'email body in plain text',
              'html' => 'email body in HTML format');
foreach ($data as $k => $d) {
    $request->addPostParameter($k, $d);
};
$request->addUpload('attach1', './sample.pdf', 'sample.pdf', 'application/pdf');
$request->addUpload('attach2', './sample.txt', 'sample.txt', 'text/plain');

$result  = $request->send();
var_dump($result);
?>

curl -F 'apiuser=el que te hemos facilitado' \
      -F 'apipass=el que te hemos facilitado' \
      -F 'from=sender@example.com' \
      -F 'to=recipient@example.com' \
      -F 'subject=asunto del mensaje' \
      -F 'text=cuerpo del correo electrónico en texto sin formato' \
      -F 'html=cuerpo del correo electrónico en formato HTML' \
      -F 'attach=@sample.pdf;type=application/pdf' \
      -F 'attach=@sample.txt;type=text/plain' \
      https://rsXXX-api.realsender.com/mail/send