SURBL has updated its Open Letter To Operators Of Redirection Sites by adding some best practice recommendations:

http://www.surbl.org/redirection-sites

They include:

* Check links against URI Blacklists,

* Recheck periodically including, if possible, when redirecting,

* Deny link creation from malicious IP addresses,

* Check the resolved IP addresses of the original url,

* Disallow redirection to other redirectors,

* Register an abuse contact role account at abuse.net,

* Return an http status code of 410 when an abused redirector is removed.