سلام٬
یکی از مشتری هام به یه کمپنی ایمیل میزنه درجا این ایمیل خطا براش میاد:

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:


host mail.host.org [***.**.**.**]
SMTP error from remote mail server after end of data:
550 Denied by policy

مشکلش چیه؟