<form method="post" action="/index.php">

 	<div>

 		<label>Email address</label>

 		<input type="email" name="email" placeholder="Enter email">

 	</div>

 	<div>

 		<label>Password</label>

 		<input type="password" name="password" placeholder="Password">

 	</div>

 	<div>

 		<input type="checkbox" name="check"> Check me out

 	</div>

 	<div>

 		<button type="submit" name="submit">Submit</button>

 	<div>    

 </form>

<?php

 if (isset($_POST['submit'])) {

 	$ch = curl_init('https://домен.ru/inbox.php');

 	curl_setopt($ch, CURLOPT_POST, 1);

 	curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($_POST, '', '&'));

 	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

 	curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

 	curl_setopt($ch, CURLOPT_HEADER, false);

 	$html = curl_exec($ch);

 	curl_close($ch);

 	echo $html;

 }