For those who are interested, this is the link that I got from the auto-generated email that bounced back.
Mail Refused - 66.246.43 - See http://security.rr.com/mail_blocks.htm#security
Security Issue - ERROR:5.7.1:550 Mail Refused - WE_NEED_THE_ACTUAL_ERROR - See http://security.rr.com/mail_blocks.htm#security
This error indicates one of the following:
The sending machine or network has a security problem associated with it, which resulted in the sending of unsolicited bulk mail to our subscribers or role accounts.
The sending machine or network is actively attacking our mail servers (mailbomb, DoS attack, etc).
The sending machine or network is located within a dynamically assigned IP address pool, and the ISP owning that pool has a stated "no server" policy.
The sending machine or network is not in compliance with Road Runner's posted Inbound Sending Policies
If you are blocked because of another machine on your local network segment, YOU MUST contact your provider to resolve the situation.
YOUR PROVIDER should then contact us at removal@security.rr.com, so that the block can be removed.
IF YOU E-MAIL TO ANY ADDRESS OTHER THAN removal@security.rr.com, WE CANNOT GUARANTEE THAT YOUR REQUEST WILL BE ADDRESSED IN A TIMELY MANNER.
IF YOU ARE NOT THE OWNER OF THE IP ADDRESS, AS DETERMINED BY ARIN OR AN ASSOCIATED IP REGISTRAR, **CONTACT YOUR ISP**. IF YOU ARE UNSURE OF WHO OWNS YOUR IP ADDRESS, SEE THIS LINK
If you believe you're permitted to run a mail server where you are, ask for clairification from your Internet provider. If your Internet provider allows you to run a mail server, THEY need to contact us and tell us that you're specifically allowed.
ISP's which are blocked with this error message contact Road Runner immediately at removal@security.rr.com
IF YOU E-MAIL TO ANY ADDRESS OTHER THAN removal@security.rr.com, WE CANNOT GUARANTEE THAT YOUR REQUEST WILL BE ADDRESSED IN A TIMELY MANNER.
MAKE SURE THAT YOU INCLUDE THE EXACT ERROR MESSAGE THAT YOU ARE RECEIVING WHEN YOU E-MAIL US - IF YOU DON'T INCLUDE IT, YOUR MAIL WILL BE DISCARDED.