XCON: Messages Sent Over X.400 Connector Should NDR First (159301)

SUMMARY

The Microsoft Exchange Message Transfer Agent (MTA) may attempt, over an X.400 connector, to deliver a message that was sent to a Microsoft Exchange mailbox that was recently removed from the system. The message will eventually result in a non-delivery report (NDR) and the sender will receive a message similar to the following:

Your message did not reach some or all of the intended recipients.

Subject: This is a test
Sent: 1/24/97 11:17:44 AM

The following recipient(s) could not be reached:

/c=US/a=ATTMAIL/p=Org/DDA:MSXCHNGE=
//o=Org//ou=Site//cn=RECIPIENTS//cn=Mailbox

on 1/24/97 11:16:59 AM

The recipient was detected looping within the message transfer service.

Microsoft has confirmed this to be a problem in Microsoft Exchange version 4.0. This problem was corrected in the latest Microsoft Exchange 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

MORE INFORMATION

This problem only happens under certain circumstances where a message has been sent from a user in a site where the intended recipient was not originally located. This could occur if someone attempts to reply to a message sent by someone who was recently removed from the mail system. Senders who reside in the same site where the intended recipient was originally located will receive an NDR immediately with a message similar to the following:

Your message did not reach some or all of the intended recipients.

Subject: This is a test
Sent: 1/24/97 11:17:44 AM

The following recipient(s) could not be reached:

'User Name' on 1/24/97 11:14:44 AM

The recipient name is not recognized.

To explain this behavior more clearly, assume there is an Exchange organization called "Org" that consists of three sites, Site A, Site B, and Site C. Both Site A and Site C are connected via site connectors to Site B which is the hub for the organization. Site B connects the organization to the rest of the world via an X400 connector. There used to be a mailbox in Site C for OldUserOnC. When a user in Site A attempts to reply to a message that had been sent by OldUserOnC prior to that user being removed from the system, the message is sent to the hub server in Site B. When the message reached the hub server, there are two parts to the recipient's address. These two parts are the DN (Distinguished Name) and OR (Originator/Recipient) addresses.

The hub first tries to resolve the full DN which may have been similar to:

/O=Org/Ou=Site C/CN=Recipients/CN=OldUserOnC

The DN no longer exists in the DS since the user's mailbox had been deleted. Thus, it then tries to resolve the OR address via a proxy lookup. It does not find a new DN based on the OR address proxy lookup. It then nulls out the original DN and then attempts to route the message out over the X400 connector where it does not match anything, and ultimately NDRs.