email being sent but not by me

Hello,

My email account seems to be sending out SPAM to my contacts.  I've verfiied that my account has not been compromised.  Can you look at the header data from an email that was rejected by a yahoo account and provide any advice?

Begin forwarded message:

From: Mail Administrator <Postmaster@cox.net>
Date: July 18, 2012 1:27:29 AM PDT
To: <I blocked my email address here>
Subject: Mail System Error - Returned Mail
Reply-To: <Postmaster@cox.net>

Your message was rejected by mta6.am0.yahoodns.net for the following reason:

    Message not allowed - [PH01] Email not accepted for policy reasons.  Please visit http://postmaster.yahoo.com/errors/postmaster-27.html [120]

The following recipients did not receive this message:

    <I blocked out the email address of my friend here>

Please reply to <Postmaster@cox.net>
if you feel this message to be in error.

Reporting-MTA: dns; eastrmfepo203.cox.net Arrival-Date: Wed, 18 Jul 2012 04:27:29 -0400 Received-From-MTA: dns; eastrmimpo209.cox.net (68.230.241.224) Final-Recipient: RFC822; <I blocked out the email address of my friend here> Action: failed Status: 5.3.0 Remote-MTA: dns; mta6.am0.yahoodns.net (66.196.118.36) Diagnostic-Code: smtp; 554 Message not allowed - [PH01] Email not accepted for policy reasons. Please visit http://postmaster.yahoo.com/errors/postmaster-27.html [120] </>

http://mywohnplus.com/appearexactly/John_Thomas47/

 

Here is an example of what is received from other people in my address book

 

 

Thanks for any help you can provide.