<?php

//Array exemplo
$emails = [
    'email1@alura.com',
    'email2@alura.com',
    'email3@alura.com',
];


foreach ( $emails as $index => $email )  {
    [  $usuarios[$index], $dominios[$index]  ] = explode( "@", $email );
}

print_r ( $usuarios );
print_r ( $dominios );