First Figure:

2.X.X Success
Success specifies that the DSN is reporting a positive delivery action. Detail sub-codes may provide notification of transformations required for delivery.

4.X.X Persistent Transient Failure
A persistent transient failure is one in which the message as sent is valid, but some temporary event prevents the successful sending of the message. Sending in the future may be successful.

5.X.X Permanent Failure
A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.

X.0.X Other or Undefined Status
There is no additional subject information available.

X.1.X Addressing Status
The address status reports on the originator or destination address. It may include address syntax or validity. These errors can generally be corrected by the sender and retried.

X.2.X Mailbox Status
Mailbox status indicates that something having to do with the mailbox has cause this DSN. Mailbox issues are assumed to be under the general control of the recipient.

X.3.X Mail System Status
Mail system status indicates that something having to do with the destination system has caused this DSN. System issues are assumed to be under the general control of the destination system administrator.

X.4.X Network and Routing Status
The networking or routing codes report status about the delivery system itself. These system components include any necessary infrastructure such as directory and routing services. Network issues are assumed to be under the control of the destination or intermediate system administrator.

X.5.X Mail Delivery Protocol Status
The mail delivery protocol status codes report failures involving the message delivery protocol. These failures include the full range of problems resulting from implementation errors or an unreliable connection. Mail delivery protocol issues may be controlled by many parties including the originating system, destination system, or intermediate system administrators.

X.6.X Message Content or Media Status
The message content or media status codes report failures involving the content of the message. These codes report failures due to translation, transcoding, or otherwise unsupported message media. Message content or media issues are under the control of both the sender and the receiver, both of whom must support a common set of supported content-types.

X.7.X Security or Policy Status
The security or policy status codes report failures involving policies such as per-recipient or per-host filtering and cryptographic operations. Security and policy status issues are assumed to be under the control of either or both the sender and recipient. Both the sender and recipient must permit the exchange of messages and arrange the exchange of necessary keys and certificates for cryptographic operations.

Third Figure:

• 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