I've been getting these bounce emails just wondering if anyone can shed light on this?
----- The following addresses had permanent fatal errors -----
<mark@**********.com>
----- Transcript of session follows -----
550 5.1.2 <mark@**********.com>... Host unknown (Name server: mx.localhost.com.cust.b.hostedemail.com.: host not found)
Final-Recipient: RFC822;
mark@localhost.comAction: failed
Status: 5.1.2
Remote-MTA: DNS; mx.localhost.com.cust.b.hostedemail.com
Last-Attempt-Date: Wed, 10 Oct 2012 01:59:02 -0400