# Enforce Flow Control

The value specified for the `flowControl` property on a destination is a target maximum for pending message storage. When flow control is enabled, the server may use slightly more or less storage before enforcing flow control, depending upon message size, number of message producers, and other factors.

Setting the `flowControl` property on a destination but specifying no value causes the server to use a default value of 256KB.

When the storage for pending messages is near the specified limit, the server blocks all new calls to send a message from message producers. The calls do not return until the storage has decreased below the specified limit, or the `flowControl` limit is increased. Once message consumers have received messages and the pending message storage goes below the specified limit, the server allows the send message calls to return to the caller and the message producers can continue processing.

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