Is there a "ready, lightweight" local mail server for debugging scripts?

Question

Mail server

Greetings!
Is there a "ready, lightweight" mail server (installation in one package that does not require a bunch of settings a la Postfix)?
Wishlist are:
1. The ability to connect ordinary clients
2. Purely "local" without using external existing accounts.
3. Easy simple installation, easy creation of test accounts.

Answer 1

If quite primitive, then in php.ini

[mail function]
sendmail_from = [e-mail]
sendmail_path = "php /path/to/sendmail_simple_emulator.php"

And inside something like:

$MailDir = __DIR__.'/log/'; // папка для сохранения писем
if (!is_dir($MailDir)) {
  mkdir($MailDir, 0644);
}

$data = "";
$line = 'foo';

$f = fopen("php://stdin", "r"); 	
while( !feof($f) AND ($line!='') ) { 
  $line = fgets($f,255); 
  $data .= $line;
} 
fclose($f);

$data = str_replace("\r", '', $data);
$data = str_replace("\n", PHP_EOL, $data);

$i = 0;
$addon = '';
while ( file_exists( $fname = ($MailDir.'/'.date('Y-m-d-H-i-s').$addon.'.eml') )) {
  $addon = '-' . ++$i;
}

file_put_contents($fname, $data);

The output is a folder with .eml files.