Magento – Newsletter Spam Subscriber

Try {{var subscriber.customer_firstname}}

Take a look at

/app/code/core/Mage/Newsletter/Model/Queue.php

/**
 * Send messages to subscribers for this queue
 *
 * @param   int     $count
 * @param   array   $additionalVariables
 * @return Mage_Newsletter_Model_Queue
 */
public function sendPerSubscriber($count=20, array $additionalVariables=array())
{
    ....

    $collection = $this->getSubscribersCollection()
        ->useOnlyUnsent()
        ->showCustomerInfo()
        ->setPageSize($count)
        ->setCurPage(1)
        ->load();

    ....

    foreach($collection->getItems() as $item) {
        $email = $item->getSubscriberEmail();
        $name = $item->getSubscriberFullName();

        $sender->emulateDesign($item->getStoreId());
        $successSend = $sender->send($email, $name, array('subscriber' => $item));

Then take a look at /app/code/core/Mage/Newsletter/Model/Resource/Subscriber/Collection.php

In my opinion it's not possible. At most you can try to check if the domain in question have MX record and try to connect to its mail server. Even that won't guarantee it is in working condition though.

You absolutely can't check if a particular e-mail exists on it in some standartized way as there are many approaches to masquerade and aliasing that many server employ. Servers can and will report in SMTP exchange non-existent addresses as valid for many reasons in both VRFY and MAIL/RCPT. The only definite answer you can get is that e-mail is invalid if it is rejected by MAIL/RCPT, but being accepted is not definite proof of it being valid, as it can be rejected down the line of e-mail processing. Abusing MAIL/RCPT without actually sending anything can also lead to you being blocked.

If you want to verify user-supplied e-mail, your best bet is to send confirmation letter there.

You also should review if you really need confirmed working e-mail at all.