OpenCart emails bounce: message has lines too long for transport

In cPanel emails from OpenCart are bouncing back with the error message: message has lines too long for transport

To fix this edit the /system/library/mail/mail.php and encase every instance of base64_encode() with chunk_split()

$message .= base64_encode($this->html) . $eol;

becomes

$message .= chunk_split(base64_encode($this->html)) . $eol;