Check your email list with the email validation service from mailboxlayer

check-email-list.php

<?php
set_time_limit(0);
ini_set('memory_limit', '2048M'); // if your list is very long
$api_key = 'PLACE HERE YOUR API';

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

$count = 0;

if (($handle = fopen("emaillist.csv", "r")) !== FALSE) {
    while (($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);

Your "basic" email list needs only a single column for the email addresses.