If you using spamassassin to reduce spam to your mail server, there is big possibilities that you are also using DCC (Distributed Checksum Clearinghouses).
If you are not (yet) use DCC in your spamassassin, than you should consider to install one.
DCC is a free software, as long as you don’t sell the device or the service to to others. Reade the DCC license here.
Installation DCC may be confusing for some people (including me 🙂 ), but when it installed and configured properly, it will catch more spam that you already catch.
The good point is, if the DCC already installed, than is easy to update it. You just need to download the updatedcc script here, and copied it to /usr/local/bin (might be different with your OS ) with the rest of DCC files.
How to update? Just run the updatedcc and the process will run automatically.
After all the process completed, do a simple check to see if your DCC already updated.
It will show the version of your DCC software.