Queue and Retry Email Delivery in PHP

Last updated: August 28, 2026.

A queue makes requests faster and protects delivery from short provider outages. Store the message intent, let a worker claim it, and distinguish temporary failures from permanent ones.

Calculate bounded backoff

<?php
function nextEmailAttempt(int $attempt): DateTimeImmutable
{
    $seconds = min(3600, 30 * (2 ** min($attempt, 7)));
    return (new DateTimeImmutable())->modify('+' . ($seconds + random_int(0, 15)) . ' seconds');
}

Prevent duplicate sends

• Claim queue rows transactionally.
• Give each logical message a unique key.
• Do not retry invalid recipients indefinitely.
• Store provider message IDs for webhooks.
• Apply a retention policy to message data.

Reference: PHP DateTimeImmutable reference.