Appendix B: Delivery Status Notification Codes

Even in the best-conceived and best-managed Microsoft Exchange environments, you are bound to have messages that just can’t make it through the system. When a message experiences a fatal error and cannot be delivered, Microsoft Exchange Server 2003 returns a non-delivery report (NDR) to the sender and optionally to an administrator.

As you’ll recall, non-delivery reports are system messages that report the delivery status of a message to the sender. (The structure of NDRs is defined in Request for Comments [RFC] 1893.) They are a subclass of a general message information structure referred to as delivery status notifications (DSNs). An NDR provides a three-digit delivery status notification code, such as 4.4.1, that identifies the failure more precisely. Each digit of the code provides information about the failure. The first digit indicates one of three different situations:

• 2.x.x Successful transfer

• 4.x.x Persistent transient failure

• 5.x.x Permanent failure

Table B-1 lists the second and third digit codes and their meanings. For example, the code 4.4.1 indicates a persistent transient failure because the host being sent the message did not answer.

Table B-1: Standard delivery status notification codes

Code	Description
x.1.0	Other address status
x.1.1	Bad destination mailbox address
x.1.2	Bad destination system address
x.1.3	Bad destination mailbox address syntax
x.1.4	Destination mailbox address ambiguous
x.1.5	Destination mailbox address valid
x.1.6	Mailbox has moved
x.1.7	Bad sender’s mailbox address syntax
x.1.8	Bad sender’s system address
x.2.0	Other or undefined mailbox status
x.2.1	Mailbox disabled, not accepting messages
x.2.2	Mailbox full
x.2.3	Message length exceeds administrative limit
x.2.4	Mailing list expansion problem
x.3.0	Other or undefined mail system status
x.3.1	Mail system full
x.3.2	System not accepting network messages
x.3.3	System not capable of selected features
x.3.4	Message too big for system
x.4.0	Other or undefined network or routing status
x.4.1	No answer from host
x.4.2	Bad connection
x.4.3	Routing server failure
x.4.4	Unable to route
x.4.5	Network congestion
x.4.6	Routing loop detected
x.4.7	Delivery time expired
x.5.0	Other or undefined protocol status
x.5.1	Invalid command
x.5.2	Syntax error
x.5.3	Too many recipients
x.5.4	Invalid command arguments
x.5.5	Wrong protocol version
x.6.0	Other or undefined media error
x.6.1	Media not supported
x.6.2	Conversion required and prohibited
x.6.3	Conversion required but not supported
x.6.4	Conversion with loss performed
x.6.5	Conversion failed
x.7.0	Other or undefined security status
x.7.1	Delivery not authorized, message refused
x.7.2	Mailing list expansion prohibited
x.7.3	Security conversion required but not possible
x.7.4	Security features not supported
x.7.5	Cryptographic failure
x.7.6	Cryptographic algorithm not supported
x.7.7	Message integrity failure