Unable to Deliver Emails to Comcast Customers

Our business is having an issue where emailed receipts sent to customers using comcast.net emails do not receive the email. Our email account receives the following error:

This is an automatically generated Delivery Status Notification.

Unable to deliver message to the following recipients, due to being unable to connect successfully to the destination mail server.

According to this thread, it seems Comcast may have blocked our emails as spam:

http://forums.comcast.com/t5/E-Mail-and-Xfinity-Connect-Help/Subject-Delivery-Status-Notification-Failure/m-p/704104

Other customers that do not use Comcast are able to receive our company's emails. Below is the full header information from a successfully delivered email with the recipient email address removed, hopefully this will be enough to unblock our emails. Let me know if we can provide further information to help resolve this issue.

Received: (qmail 5629 invoked by uid 30297); 19 Feb 2015 17:31:55 -0000
Received: from unknown (HELO p3plibsmtp03-02.prod.phx3.secureserver.net) ([68.178.213.114])
          (envelope-sender )
          by p3plsmtp21-05.prod.phx3.secureserver.net (qmail-1.03) with SMTP
          for <>; 19 Feb 2015 17:31:55 -0000
Received: from freedonationkiosk.com ([66.135.63.10])
	by p3plibsmtp03-02.prod.phx3.secureserver.net with bizsmtp
	id uHXu1p01v0DFzsa01HXvD2; Thu, 19 Feb 2015 10:31:55 -0700
Received: from mail pickup service by freedonationkiosk.com with Microsoft SMTPSVC;
	 Thu, 19 Feb 2015 11:31:54 -0600
MIME-Version: 1.0
Sender: "FreeGivingkiosk" 
From: "FreeGivingkiosk" 
To: 
Date: 19 Feb 2015 11:31:54 -0600
Subject: Donation Receipt: Thank you for Donation