The use of "undisclosed-recipients:;" in lib/ezutils/classes/ezmail.php and lib/ezutils/classes/ezsendmailtransport.php results in a Delivery Failure Error.

Steps to reproduce

• Setup a simple, out of the box Create/Approve workflow
• Make a change to a content object
• User and Approver both receive emails but admin for the server on which sendmail used by ez resides, receives a Delivery Failure Error with the contents of one of the mails sent to the user/approver.