Kelimeleri veya Cümleleri Harflere Bölmek

<?php
$mail = "ulusanyazilim@gmail.com";
$bol1 = str_split($mail);
$bol2 = str_split($mail, 5);
print_r($bol1);
print_r($bol2);
?>
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Array
(
    [0] => u
    [1] => l
    [2] => u
    [3] => s
    [4] => a
    [5] => n
    [6] => y
    [7] => a
    [8] => z
    [9] => i
    [10] => l
    [11] => i
    [12] => m
    [13] => @
    [14] => g
    [15] => m
    [16] => a
    [17] => i
    [18] => l
    [19] => .
    [20] => c
    [21] => o
    [22] => m
)
Array
(
    [0] => ulusa
    [1] => nyazi
    [2] => lim@g
    [3] => mail.
    [4] => com
)
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX