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If any of the dependencies required to enable the transport listener or the sender are missing, the transport will not be enabled and you will be redirected to the Transport Management page. You will notice that the Enable option is still available for that particular transport listener or sender, indicating that it hasn't been enabled. Therefore it is important that you put all the required jars in the <CARBON <PRODUCT_HOME>/repository/components/dropins directory before attempting to activate a transport listener or a sender.
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