PHP/MySQL Function result in a variable, e-mail checking - php

Question

How can I use another function to check if the email is in the right format ([number of symbols]#[number of symbols].[number of symbols]) and if it's unique while adding it using the insertUser? (All info is read from a .txt file).
Code:
class User{
function randomPassword($length = 8){
$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$randomString = '';
for ($i = 0; $i < $length; $i++) {
$randomString .= $characters[rand(0, strlen($characters) - 1)];
}
return $randomString;
}
function insertUser($firstName, $lastName, $email){
global $DB;
$DB->query("INSERT INTO `users` (`fname`, `lname`, `password` , `email`) values ('$firstName', '$lastName', '" . randomPassword() . "', '$email') ");
}
In the index file:
$USER = new User();
$data = readData();
foreach($data as $nr => $user){
$USER->insertUser($user['first_name'], $user['last_name'], $user['email']);
}

Answer 1

Call as $this->randomPassword();
Email validation
function checkEmail($email) {
if(preg_match("/^([a-zA-Z0-9])+([a-zA-Z0-9\._-])
?*#([a-zA-Z0-9_-])+([a-zA-Z0-9\._-]+)+$/",$email)){
list($username,$domain)=split('#',$email);
if(!checkdnsrr($domain,'MX')) {
return false;
}
return true;
}
return false;
}

Answer 2

To insert the random string you should do this :
Change the insertUser function to :
function insertUser($firstName, $lastName, $email){
global $DB;
$DB->query("INSERT INTO `users` (`fname`, `lname`, `password` , `email`) values ('$firstName', '$lastName', '" . $this->randomPassword() . "', '$email') ");
}