How do you have the "from" address configured? The email must be From a valid email address on your domain. It can be a forward only, but beware forwarding to a non-dreamhost domain may mean mid flagged mail, if it's a forward only stick with an address/mailbox on your account.
Many plugins by default are set to use the submited email address as the from address, that won't work. For example, your not @gmail.com therefore your dreamhost account can't send email is if it were gmail.