+PH/12 In a pipe transport, although a timeout while waiting for the pipe
+ process to complete was treated as a delivery failure, a timeout while
+ writing the message to the pipe was logged, but erroneously treated as a
+ successful delivery. Such timeouts include transport filter timeouts. For
+ consistency with the overall process timeout, these timeouts are now
+ treated as errors, giving rise to delivery failures by default. However,
+ there is now a new Boolean option for the pipe transport called
+ timeout_defer, which, if set TRUE, converts the failures into defers for
+ both kinds of timeout. A transport filter timeout is now identified in
+ the log output.
+