What settings are you using? Have you made sure the FROM address is one that is hosted here at DreamHost? http://dhurl.org/20b
You can also check your web server's maildir for any bounces there. If you're seeing any error messages please paste those here too.
You can also reach out to our support team directly with your details so they can take a deeper look into your account/settings: http://dhurl.org/dhsupport