Reads the AS1 request from the mail server.
public func readRequest() throws -> Void
In the Java edition, ReadRequest will retrieve the file specified by MailMessageNumber from the mail server. The request will be stored in Request and the headers in RequestHeaders. The headers will also be parsed as in ParseHeaders, and the appropriate values of From, SendTo, etc., will be populated. After looking up and setting your trading partner information (such as certificates) you may then call ProcessRequest.