Magento Email – Fix Email Notification Not Delivered to Customers

First go to System > Configuration > Sales Emails and make sure that Enabled is set to Yes.

After that look in core_email_queue table. If there are entries in the table and customers/admin are not getting any emails it means cron job is not running.

More details here.

From Outside Magento.

If you want to send All Customers Reset Password Email, then below is the code.

//place this before any script you want to calculate time
$time_start = microtime(true);

// MAGENTO START
include('app/bootstrap.php');

use Magento\Framework\App\Bootstrap;
use Magento\Customer\Api\AccountManagementInterface;
use Magento\Customer\Model\AccountManagement;

$bootstrap = Bootstrap::create(BP, $_SERVER);
$objectManager = $bootstrap->getObjectManager();

$state = $objectManager->get('Magento\Framework\App\State');
$state->setAreaCode('frontend');

$_customers = $objectManager->create('Magento\Customer\Api\AccountManagementInterface');
$customerCollection = $objectManager->create('Magento\Customer\Model\ResourceModel\Customer\Collection');
$customerCollection->load();
$i = 0;
foreach ($customerCollection as $customers) {

    $email = $customers->getData('email');

    try {
            $_customers->initiatePasswordReset($email, AccountManagement::EMAIL_RESET);
        } catch (NoSuchEntityException $e) {
            // Do nothing, we don't want anyone to use this action to determine which email accounts are registered.
        } catch (\Exception $exception) {
            echo __('We\'re unable to send the password reset email.');
        }
        echo "<pre>";
        echo $i . " Email :-" . $email . " Mail Sent";
    $i++;
}

echo "<pre>";
echo "Total Customers: " . $i;

$time_end = microtime(true);

//dividing with 60 will give the execution time in minutes other wise seconds
$execution_time = ($time_end - $time_start) / 60;

//execution time of the script
echo "<pre>";
echo 'Total Execution Time:</b> ' . $execution_time . ' Mins';

Hope it helps Magento Community :)