The present invention provides for flow and congestion control mechanisms in accordance with a Reliable Message protocol for Web Services (RM-WS). For flow control, one endpoint informs another endpoint of its available buffer size by including buffer size information in response messages. The response messages, typically RM-WS infrastructure messages, are then used to determine an upper limit on the number of messages that can be sent to the acceptor in order to prevent resending messages due to buffer overrun. In the case of congestion control, embodiments provide for increasing the number of in-flight messages until a failure point is found. The last successful rate below the failure point is the closest known point to the optimum point. Example embodiments then reset and try again raising the rate back to the last known good point and fine tuning from there using an algorithm that asymptotes the optimum rate.