Gets and optionally downloads the next unread fax (if one is available) and returns the FaxReceive information. The {download} parameter may be set to 1 or 0 when using this function. This function is designed for multi-process environments that attempt to receive a fax using the same account. To resolve contention, only one peer may gain access to an unread fax at a time. If the peer fails to download the fax and mark it as received within a 5-minute window, the automatic lock on the fax is released and another peer may download the unread fax. Additionally, the peer may also set the {sid} parameter which is a GUID representing the site-id. etherFAX will record the site id responsible for downloading the fax document.