From publicly available information, my understanding is that Dreamhost doesn't offer email only accounts.
I'd personally suggest using Google Apps for your email. You will have to use a third-party DNS service as well since you only get the full DNS service features with a Dreamhost hosting account.
I don't have a recommendation for DNS services anymore, but freedns, zoneedit, and everydns come to mind. I use zoneedit but I've heard their service had declined after they got bought out.
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