<?php
$numbers = array("a421zx", "asfqe", "l228ol");

$matches = array();

$regexp = '/^[a-z][0-9]{3}[a-z]{2}$/';

foreach ($numbers as $number){
	if (preg_match($regexp, $number, $matches)) {
	    	echo "All right:\n";
	    	echo "$number\n";
	    	echo "---------------\n";
	} else {
		echo "Uncorrectly. Please, kill yorself:\n";
		echo "$number\n";
		echo "---------------\n";
	}
}