A user is trying to send an email to a specific domain, but when they do they receive a kickback.
I tried googling this but could not find much in the way of information. Could it be that the receiving domain is marking us as spam and rejecting it?
Your message did not reach some or all of the intended recipients.
The following recipient(s) could not be reached:
User@Domain.com on 4/8/2009 8:05 PM
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
< Server.MyDomain.com #5.0.0 X-Proprietary; host smtp03.Domain.com[184.108.40.206] said: 551 5.0.0 SPAM NOT ALLOWED (in reply to end of DATA command)>