Email Not Working.

I have just changed the following code at system/library/mail.php

Original:
$header .= 'Date: ' . date('D, d M Y H:i:s O') . $this->newline;
$header .= 'From: ' . '=?UTF-8?B?' . base64_encode($this->sender) . '?=' . ' <' . $this->from . '>' . $this->newline;
$header .= 'Reply-To: ' . '=?UTF-8?B?' . base64_encode($this->sender) . '?=' . ' <' . $this->from . '>' . $this->newline;
$header .= 'Return-Path: ' . $this->from . $this->newline;
$header .= 'X-Mailer: PHP/' . phpversion() . $this->newline;
$header .= 'Content-Type: multipart/related; boundary="' . $boundary . '"' . $this->newline . $this->newline;

Changed:
$header .= 'Date: ' . date('D, d M Y H:i:s O') . $this->newline;
//$header .= 'From: =?UTF-8?B?' . base64_encode($this->sender) . '?=' . ' <' . $this->from . '>' . $this->newline;
$header .= 'From: email@yourdomainname.com' . $this->newline;
if (!$this->reply_to) {
$header .= 'Reply-To: =?UTF-8?B?' . base64_encode($this->sender) . '?=' . ' <' . $this->from . '>' . $this->newline;
} else {
$header .= 'Reply-To: =?UTF-8?B?' . base64_encode($this->reply_to) . '?=' . ' <' . $this->from . '>' . $this->newline;
}
$header .= 'Return-Path: ' . $this->from . $this->newline;
$header .= 'X-Mailer: PHP/' . phpversion() . $this->newline;
$header .= 'Content-Type: multipart/related; boundary="' . $boundary . '"' . $this->newline . $this->newline;