Magento – How to delete email recipients from database

You will need a resource model with a method that returns true if the customer email is already registered.

Thankfully, this is already implemented both for customers and for email signups:

Newsletter Signup:

$subscriber = Mage::getModel('newsletter/subscriber')->loadByEmail($email);
if($subscriber->getId()){
//your logic
}

Customer Registration:

$customer = Mage::getModel('customer/customer')->loadByEmail($email);
if($customer->getId()){
//your logic
}

See how this is implemented in a resource model below:

public function loadByEmail(Mage_Customer_Model_Customer $customer, $email, $testOnly = false)
{
    $adapter = $this->_getReadAdapter();
    $bind    = array('customer_email' => $email);
    $select  = $adapter->select()
        ->from($this->getEntityTable(), array($this->getEntityIdField()))
        ->where('email = :customer_email');

    //... removed some website scope stuff for brevity

    $customerId = $adapter->fetchOne($select, $bind);
    if ($customerId) {
        $this->load($customer, $customerId);
    } else {
        $customer->setData(array());
    }

    return $this;
}

As you can see, the heavy lifting is in the $adapter->select() which is limited to the where clause that only loads customers by a singular email address. Then fetchOne is called, which, if it returns anything at all then loads a customer.

In your case, a simple return true would alert you to whether the email exists or not. What you do after that is up to the specific requirements of your task and application.

1. Starting with Magento 1.9.1 the emails are not being sent directly during checkout but instead are being queued.
2. The queue is being processed via your Magento cronjob - please ensure this has been set up and is running correctly.
3. The extension AOE_Scheduler can help you in confirming that your Magento cronjob has been configured correctly and is running.