Spam filtering does not seem to be working well and I am seeing "URIBL_BLOCKED" listed in the Spam Report for a lot of emails in MailControl.

If you are seeing "URIBL_BLOCKED" frequently in the Spam Report for emails in MailWatch, it means that the nameserver you are using is not allowed to access certain RBLs via SpamAssassin. In this case you may want to switch to using a local nameserver if you are able to. This is a two step process. 

1) IMPORTANT: For your DNS to continue working with this configuration, you must first configure named to run as a local caching nameserver on your server (i.e. you must make sure that you allow localhost DNS recursion in /etc/named.conf - your server admin should be able to do this if it is not already configured this way).

2) Add 127.0.0.1 as the first nameserver listed in /etc/resolv.conf, like this:

nameserver 127.0.0.1

If you make this change and have not already been manually training your bayes database, you might want to reset your bayes database at the same time so that it becomes more accurate more quickly. Instructions are in this FAQ.