Well this is odd, because I can send an e-mail without authentication from my Dreamhost user via localhost, and the e-mail arrived.
$ telnet localhost 25
Connected to localhost.
Escape character is '^]'.
220 ps9296.dreamhostps.com ESMTP
250 2.1.0 Ok
250 2.1.5 Ok
354 End data with <CR><LF>.<CR><LF>
250 2.0.0 Ok: queued as CA38D62E84D0
221 2.0.0 Bye
Connection closed by foreign host.
On second thought, I suppose it's because I am on a VPS and the restriction is probably only for shared hosting.