I’m assuming that harlem.dreamhost.com is a shared web hosting server.
RR won’t accept email from THAT server. Probably due to prior spam originating from that IP address (harlem).
It’s fairly common at dreamhost to find web hosting machines with email blocks/blacklists. It’s less common (but still possible) for dreamhosts email servers to be on blacklists.
I don’t know what is SENDing your email, or why it’'s being “forwarded” FROM web hosting machine (as opposed to a dreamhost email server) but the best way to approach this is if the email is being sent FROM a web application configure that web application to use SMTP and give it the credentials of an actual email account at dreamhost to send the email.