What are the potential bottlenecks and performance considerations when using PHP for sending personalized emails to a large number of recipients?

When sending personalized emails to a large number of recipients using PHP, potential bottlenecks can arise from inefficient code execution, database queries, and network latency. To improve performance, consider optimizing your code by batching email sending, caching database queries, and using a third-party email service provider for bulk sending.

// Example code snippet for batching email sending
$recipients = array(); // array of recipients
$batchSize = 100; // number of emails to send in each batch

foreach (array_chunk($recipients, $batchSize) as $batch) {
    foreach ($batch as $recipient) {
        // code to send personalized email to $recipient
    }
}