1. A web-services provider, comprising: a web server for hosting web-services provided by the web services provider, the web services provider providing a web-services interface accessible by a web-services requestor over a network, the web-services interface defining: a message binding extension element operable to specify a format for a message transmitted to the web-services provider by the web-services requestor requesting said web-service; and a binding details extension element operable to specify an availability status of at least one receipt for said message, wherein the web server determines whether the message includes a valid delivery receipt request by determining whether the web-services interface requires a delivery receipt request to be included in the message by checking an attribute of the binding details extension element in the web-services interface, and if not, determining whether the web-services interface prohibits the delivery receipt request from being included in the message by checking the attribute.