I will be glad to pass your feedback along to our SmarterMail team.
SmarterMail does have configurable settings to restrict when the Auto-Responder is sent out. If you sign into the SmarterMail web interface and navigate to Settings -> Antispam -> Options, here you should see a setting for AutoResponders, you will want to ensure this options is set to 'Require Message Pass SPF' this will ensure that any user sending to a user with autoresponders must first pass an SPF check before sending the autoresponder out. If a sender comes in spoofing a From address from an unauthorized IP address, the autoresponder will not send out.
This will prevent you from landing on the BackScatter RBL, as well as being blacklisted with various IP's for sending unauthorized auto-responders.
I hope this helps.
Technical Support Supervisor