Bounce codes can be categorized as follows (http://tools.ietf.org/html/rfc3463):
Types
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Soft |
A soft bounce is a persistent transient failure. The message as sent is valid, but some temporary event prevents the successful sending of the message: the inbox of the user can be full, a network error occurs, ... |
|
Hard |
A hard bounce is a permanent failure. This bounce 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. |
Category
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Addressing |
There is a problem with the originator or destination address, such as address syntax or validity. |
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Mailbox |
There is a problem with the receiver's mailbox. |
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Mail system |
There is a problem with the destination system. |
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Network and routing |
There is a problem with the delivery system, such as the network, the routing, or the directory. |
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Mail delivery protocol |
There is a problem with the message delivery protocol. These failures include the full range of problems resulting from implementation errors or an unreliable connection. |
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Message content or media |
There is a problem with the content of the message. These codes report failures due to translation, transcoding, or otherwise unsupported message media. |
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Security or policy |
There is a problem with a policy, such as per-recipient or per-host filtering and cryptographic operations |