Check your old mailing list with the Mailboxlayer API and the results in a CSV file

check-old-mailing-list.php

<?php
set_time_limit(0);
ini_set('memory_limit', '1024M'); // should be enough for thousands of email addresses
$api_key = 'YOUR MAILBOXLAYER API KEY';

$fp = fopen('emails-checked.csv', 'w');
fputcsv($fp, array('Email address', 'Valid MX', 'Valid SMTP', 'Score'));

$count = 0;

if (($handle = fopen("emails-need-to-be-checked.csv", "r")) !== FALSE) {
    while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
		$ch = curl_init('https://apilayer.net/api/check?access_key='.$api_key.'&email='.$data[0]);
		curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
		$json = curl_exec($ch);
		curl_close($ch);
		$validationResult = json_decode($json, true);
		$row = array($data[0], $validationResult['mx_found'], $validationResult['smtp_check'], $validationResult['score']);
		fputcsv($fp, $row);
		$count++;
		if ($count % 4 == 1) sleep(1); // Don't reach the 300 requests/minute rate limit
	}
}
fclose($fp);

We use this snippet for mailing list which hasn't been user for more than 6 month. This way we keep the bounce rate for email campaigns very low.
Read our blog post about email address validation to learn more about the Mailboxlayer API.

Your emails-need-to-be-checked.csv file should contain only the email address (one for each row).