First of all, "fromClient" is not a "queue", it's a channel (although in this case, a QueueChannel). It has no bearing on the real JMS queue "queue.fromClient".
JMS doesn't have any standard notion of flow control; that's up to the broker (ActiveMQ etc). Setting a limit on the channel's queue has no bearing on whether or not ActiveMQ will stop a message from being posted. Spring Integration (via the poller in this case) will pump out as many messages as the broker will accept - it's up to the broker to impose any flow control - Spring Integration has no control over it. You have to explore your broker of choice for how to deal with this situation.
Hope that helps.
Gary P. Russell
Spring Integration Team
SpringSource, a division of VMware