Do you have dreamhost spam filter enabled? https://panel.dreamhost.com/index.cgi?tree=mail.junk&
if so, then try disabling it and test.
Also if you haven't already, you might ask support via a ticket if they know anything.
As far as I know, Unreceived/unbounced email is a new complaint, it's at least not a common complaint, that said-- dreamhost email service is far from stellar. I've shifted elsewhere for email.