Deadlettering
In a messaging system deadlettering is an action that is
taken on messages, typically when they cannot be processed by a messaging
system or by a receiving application. The Enterprise Integration Patterns book
describes two patterns that can be used for scenarios where messages cannot be
processed.
Dead
Letter Channel
The dead letter channel pattern is used when a messaging
system determines when it cannot process a message. This could be due to the
message expiring by exceeding its time to live threshold, or by some error in
the message processing system.
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The Enterprise Integration Patterns website provides a description of
the Dead Letter Channel pattern here.
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Invalid
Message Channel
The invalid message channel pattern is used when a receiving
application decides that a message cannot, or should not be processed. This
could be due to the message being formatted incorrectly, or not complying with
business rules.
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The Enterprise Integration Patterns website provides a description of
the Invalid Message Channel pattern here.
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Whilst very similar the key different in the two patterns is
that the dead letter channel is used by the messaging system and the invalid
message channel by the receiving application.