This tool can be used to verify domains in Swot project (https://github.com/leereilly/swot) by checking A/AAAA and MX records for them. It's horribly written in 10 minutes, but works ;)

CheckSwotDomains.php

<?php
define('DOMAINS_DIRECTORY', 'lib/domains/');

function path2Domain($path, $prefix = DOMAINS_DIRECTORY)
{
    $prefixPos = strpos($path, $prefix);
    if ($prefixPos !== 0) {
        throw new InvalidArgumentException('Path does not begin with given prefix');
    }

    $path = substr($path, strlen($prefix), -4); //Removes prefix & extension
    $pathParts = array_reverse(explode('/', $path));

    return implode('.', $pathParts);
}

function getDomainStatus($domain)
{
    $records = dns_get_record($domain, DNS_A + DNS_AAA + DNS_MX);

    if ($records === false) {
        return false;
    }

    $ip = 0;
    $mx = 0;
    foreach ($records as $record) {
        if ($record['type'] === 'A' || $record['type'] === 'AAAA') {
            $ip++;
        } elseif ($record['type'] === 'MX') {
            $mx++;
        }
    }

    return ['ip' => $ip, 'mx' => $mx];
}

$directory = new RecursiveDirectoryIterator(DOMAINS_DIRECTORY);
$iterator = new RecursiveIteratorIterator($directory);
$regex = new RegexIterator($iterator, '/^.+\.txt$/i', RecursiveRegexIterator::GET_MATCH);

foreach ($regex as $path) {
    $domain = path2Domain($path[0]);
    echo $domain . " - ";
    
    $records = getDomainStatus($domain);
    if ($records === false) {
        echo "DNS ERROR!\n";
        continue;
    }

    $isError = false;
    if ($records['ip'] === 0) {
        echo "[Missing website] ";
        $isError = true;
    }

    if ($records['mx'] === 0) {
        echo "[Missing MX] ";
        $isError = true;
    }

    if (!$isError) {
        echo "OK";
    }

    echo "\n";
}