Log in to SmarterMail interface for your domain name (http://mail.yourdomain.com) using your full email address and password.
Step 1: Click the 'Settings' tab in the top navigation bar
Step 2: Expand the 'My Settings' node if it isn't already and click 'Auto-Responder'
Step 3: Check the 'Enable auto responder' option
Step 4: Click the 'Auto Responder Message' tab
Step 5: Create a subject and body for your auto responder
Step 6: Click the 'Save' button near the top
To turn off the auto responder when it's no longer needed, uncheck the 'Enable auto responder' option under the 'Options' tab.