title: Send Email - ESMTP Remote Server - Access Denied, but works for coworker
body: <p>I'm trying to send an email to a client, with an address @comcast.com</p>
  
  <p>Within 4 seconds I get an email in my Inbox saying the message failed delivery.</p>
  
  <p>A coworker sitting 10 feet away from me can send emails to this address successfully.  We are on the same domain and network.</p>
  
  <pre><code>Delivery has failed to these recipients or groups:
  
  xxxxx-xxxx@comcast.com  (yes, the name has a hyphen in it)
  
  A problem occurred while delivering this message to this email address. Try sending this message again. If the problem continues, please contact your helpdesk.
  
  The following organization rejected your message: ESMTP.
  
  xxxxx-xxxx@comcast.com
  
  ESMTP
  
  Remote Server returned '&lt;ESMTP #5.0.0 smtp;550 Mailbox unavailable or access denied - &lt;xxxxx-xxxxx@comcast.com&gt;&gt;'
  </code></pre>
  
  <p>If any further information is needed please let me know.</p>
  
  <hr>
  
  <p>Does this seem like a problem at the clients end or on our side?</p>
  
  <p>Any ideas as to the cause? I don't see any detail about my access was denied...  no space, spam, blacklist, etc.?</p>