A network adapter and corresponding method for its use are disclosed. The network adapter has an operational mode that allows a host CPU to offload transmission of a block of data to the adapter. The adapter segments the block into fragments, and builds a data packet for each fragment. The adapter transmits these packets with an adapter-implemented flow control. This flow control uses: a context engine that tracks flow control variables for a “context” established for the block; a context memory for storing the variables; and a receive filter that updates flow control information for the block based on ACK packets received from the remote endpoint receiving the data packets. Because the network adapter implements flow control for data blocks that the network adapter segments, intermediate ACK packets corresponding to that block can be intercepted by the adapter, before they pass to the host, conserving host resources. An added advantage is that the host CPU can offload data blocks larger than the remote endpoint's receive window size, since the adapter can follow the transmit window and transmit packets at appropriate intervals. This further decreases load on the host CPU, decreases latency, and improves bandwidth utilization.