Blacklist

I'm not sure how to get to the blacklist and remove something, nor am I skilled enough to attempt it without some down to earth instruction, however, someone has blacklisted "blog.com" which is a strange one to block. Several blogs are listed as something like http://thisismyblog.com and while I'm not sure if this is correct, I've had a few folk tell me they can't get through because the filter bans blog.com

Help?