Up to you - but rather than whitelist - which means allow everything from that all the time no matter what.
I would have simply removed it from the blacklist. This way it can still get auto-added later by some 3rd party/blacklist if that domain become especially Spammy in the future.
To be honest, depending on where the "filter" was setup - I don't know how useful filtering messages from *@biz.rr.com are at all. If it's filtering by SMTP server, then anything biz.rr.com sends may also lead to allot of false positives.
Depends on your user base / emails you expect to get, I suppose.
