If you are getting responses to emails you haven’t sent or people querying the email you just sent, you may well have hackers accessing a script on your ecommerce site without your knowledge. I’ve recently experienced this problem and know another person who has also. The reason for this is the spammers/hackers have accessed the ‘Tell a Friend’ script on your commerce site.
For my part I didn’t even know that script had been installed so it came as a bit of a shock as I’ve always been against the ‘Tell a Friend’ thing and have denied using it for clients. Needless to say I’ve had the script removed. It had been installed when I’d had my shopping cart service updated.
If you do a Google for ‘tell a friend hack’ you’ll find quite a few posts at different forums where others have experienced the same problem. It’s obviously rife at the moment. Check carefully with the people handling your ecommerce on your site and if in doubt, then don’t. Better safe than sorry.