Hi, We run Exchange Server 2003 SP2in a cluster environment (active/passive node), on windows 2003 sp1. Exchange Virtual server has been running fine on both nodes, until recently when issues have occurred on one of the exchange nodes. When we failover to the standby node, it becomes active, and all seems well, until you try and read a new email in outlook 2003, or even send an an email internally or externally. The error message from System Administrator when sending internal or external emails is:- Subject: Undeliverable: Delivery Status Notification (Failure) message did not reach some or all of the intended recipients. Subject: The following recipient(s) could not be reached: MailboxNameon 30/08/2008 18:00 The e-mail address could not be found. Perhaps the recipient moved to a different e-mail organization, or there was a mistake in the address. Check the address and try again. <mailgate.x.x.x.x #5.1.0> However all works fine from the other exchange node. I have tried re-installing exchange on the problem node. I have also checked the permissions on the node. I can't seem to locate the issue. Please help if you can. This problem occurs when you try to send to anybody, even if they have a mailbox internally or externally. Nicole

Hi, Please check my below troubleshooting suggestions. Cause analyze ============ The NDR code 5.1.0 indicates a general categorizer-based failure (bad address failure). An e-mail address or other attribute could not be found in the directory. Two situations as below described will generate this error code. 1. This issue occurs most frequently when MDAccess receives "object not found" errors from DSAccess when the Categorizer is doing the homeMDB lookup on a user. 2 . This issue may occur if contact entries do not have the TargetAddress attribute set. Troubleshooting ============= 1. Examine the event logs on the Exchange Server node for errors. 2. If you do not find any events that let you resolve the problem, consider turning up diagnostic logging on the MSExchangeTransport Categorizer to Maximum. When diagnostic logging is enabled, re-check the event log for errors. If configuring diagnostic logging to maximum does not produce any event log entries, configure diagnostic logging to level 7 using the registry. When set to level 7, Event ID 9000 generated by the Message Categorizer will be logged, which details the function, the reason for failure, the name of the recipient that failed, and the type of recipient. To set diagnostic logging to level 7: a. Open a registry editor, such as Regedit.exe or Regedt32.exe b. Navigate to: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeTransport\Diagnostics c. In the right pane, double-click 2 Categorizer, set the value data to 7, and then click OK. d. Close the registry editor. Note: When you have completed troubleshooting, reset the value data for 2 Categorizer back to 0. 3. Verify that the Exchange Server has connectivity to one or more global catalog servers. The Network Monitor tool in Windows is very useful for this. 4. Use Message Tracking to troubleshoot messages that are stuck in the categorizer. 5. Use DCDIAG and NETDIAG tool on the Exchange node to verify if any error to access GC. 6. Use the Archive Sink tool to archive and analyze messages coming into and moving out of Exchange Server. 7. Monitor the categorizer performance counters using System Monitor. More information, please check below article: ================================ SMTP message failure warning - Categorizer address lookups not found If anything is unclear, please let me know. -Jason