Is Mcrypt output only lowercase?

Can I specify line output only when using Mcrypt?

This is a sample of my code that is used for encryption:

 public  function encode($value){ 
      if(!$value){return false;}
      $text = $value;
      $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
      $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
      $crypttext = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $this->skey, $text, MCRYPT_MODE_ECB, $iv);
      return trim($this->safe_b64encode($crypttext)); 
  }

The reason for this is that I need a lowercase only encrypted string.

Thank,

Chris.

EDIT

I am creating a response through an email application that allows users to respond to a stream through an email notification. I use a unique encrypted string as a response letter to identify it. Mcrypt prints uppercase and lowercase strings. This works great for Gmail and Outlook, but Hotmail converts the response address string to lowercase and then decryption errors. So I need the output line from func above to be only lowercase.