If I were to say 'please', would that make it more possible ? ~~
Here is one solution, for SMTP, you need to have the client send the message to an email server for holding purposes, then you write a POP3 poller in Java and then use the ServiceInvoker to call an ESB Service.
The custom_action quickstart demonstrates the ServiceInvoker:
Alright, thanks. I'll give it a shot.