I've written a simple example that shows how a Gmail account could be polled by the UltraESB and then forward them to a Web service. The example invokes the SimpleStockQuoteService hosted via the test ToolBox.
The UltraESB makes it easy to strip all unwanted email headers, and then send the request as a SOAP request by updating the content type to text/xml. The response is then sent back to the original client using Gmail SMTP
Read the full example and download the sample configuration files from here