We are trying to send emails to an email address firstname.lastname@example.org and get the following error. Can someone help me understand why we are getting this error.
From: Mail Delivery System [mailto:Mailer-Daemon@localhost.localdomain]
Sent: Tuesday, October 16, 2012 1:14 PM
Subject: Mail delivery failed: returning message to sender
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
SMTP error from remote mail server after RCPT
host mx1.xxxx.k12.mt.us [69.51.X.X]: 554 5.7.1
Client host rejected: envelope policy RBL PTRNUL
------ This is a copy of the message, including all the headers. ------
------ The body of the message is 406334 characters long; only the first
------ 106496 or so are included here.