I want to start using the built-in messaging system to to communicate with my customers. I open a customer's profile and click on "Send a message" button in "Messages and communication history" area down there.

1. How to change the default subject from "Re: Customer Name" to something meaningful(I prefer to have a text-box for it)?
2. How to use different outgoing email servers for different users? I want the message to be sent from my loged-in user's email address not a general email address.