When you email from Matrix, you are technically emailing off of the Matrix email server, but we mask it with your personal email address. So, when your recipient gets the email, it shows as having come from you, and if they reply to the email, the reply will go back to your email address.
In order to change your reply to: email address, go to the Member Dashboard (the screen that comes up when you log into www.smartmls.com).
Click the Edit button next to My Profile:
Go to the Contact Information section and adjust the MLS E-mail (for Matrix) field.
Remember to click Update when you are finished.