This page explains how to change your Spam Control daily digest preferences.
"Send digest with new messages in my End User Digest" checkbox: Checking this box will enable you to receive a Daily Digest each morning.
"Send digest even when I have no messages in my End User Digest" checkbox: Checking this box will allow you to receive a Daily Digest even if you had no spam messages caught and placed in Quarantine in the past 24 hours.
It is very important to have one or both of these boxes checked if you are in the Cautious, Cautious Plus, or Aggressive Personal Spam Policy because you should review the contents of your Quarantine periodically to make sure no legitimate email was caught.
If you are using the Tag and Deliver or No Quarantine, you will not have spam put in your Quarantine. Unchecking either of these checkboxes will stop you from receiving a Daily Digest. When you need to change your Spam Control option, you can also use the web interface to go into your policy options.