Morning all I have a strange one. I created two users (callblockerone, callblockertwo) in there own organizational unit (callblocker, as that is the domain that they are associated with) with email accounts in a separate storage group two as these are separate from the normal company day to day workings. The logon account created ok, the second account has email addresses, including the x400 address assigned to it but no mail box. When a user send a mail to the second account, I get the follow NDR From: System Administrator Sent: 06 July 2005 10:27 To: callblockertwo Subject: Undeliverable:Delivery Status Notification (Failure) Your message did not reach some or all of the intended recipients. Subject: The following recipient(s) could not be reached: callblockertwo on 06/07/2005 10:27 A configuration error in the e-mail system caused the message to bounce between two servers or to be forwarded between two recipients. Contact your administrator. <jupiter.ukdata.local #5.4.6> I also get the following in the event logs Event Type: Error Event Source: MSExchangeTransport Event Category: NDR Event ID: 3020 Date: 06/07/2005 Time: 10:27:10 User: N/A Computer: JUPITER Description: A non-delivery report with a status code of 5.4.6 was generated for recipient x-ex;/O=UK DATA/OU=FIRST ADMINISTRATIVE GROUP/CN=RECIPIENTS/CN=Callblockertwo (Message-ID <22ED2875F95FCC439CB5399211D1F7F04193C4@xxxxxxxxxxxxxxxxxxxx>). Cause: A forward loop was detected by the categorizer. This is a common hosting configuration problem caused when someone uses the provisioning tool to create a contact in one organization unit and creates a user in a different organization user that share the same e-mail address. Solution: Verify that you do not have a user in organizational unit and a contact in a different organizational unit that have the same e-mail address. For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp. Data: 0000: 46 05 04 80 F..? I have checked all users to ensure that they also don't have the callblockertwo email address. And they don't. I have checked on the Microsoft support site and eventide.net site and they only thing they refer to is public folder replications Anybody able to give me an idea to solving this? setup is Windows 2003, Exhange 2003 SP1 + plus all windows and exchange hotfixes too Simon This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify admin@xxxxxxxxxxxxxxx The views expressed in this email are those of the individual and not necessarily those of UK Data IT This footnote also confirms that this email message has been swept by SOPHOS AV for the presence of computer viruses. Web site: www.ukdatait.co.uk Registered Office: UK Data IT House, Shrub HIll Road, Worcester, WR4 9EF Registered Company Number: 3884834