Disappointing spam detection performance - expectation?

Cheer,

I am running Internet Security on Windows 7 Pro and Windows 8.1 workstations and using the Outlook client on both for email on both machines.

After using this products for a number of years, it seems that the spam detection portion of this product doesn't work very well.  Over the last 6 months, I continue to receive the same spam requests event though I go through my email each day and mark the roughly 50 or so spam emails as "This is Spam" via the Outlook plugin.   Unfortunately, I continue to receive the same number of spam emails each day.

As  an experiment, I took one of my email accounts and started using Gmail as a method to collect email via IMAP on one account.  The spam I see each day on this account has dropped to nearly zero.

Although no tool is perfect for detecting spam, I am disappointed in the amount of spam I must wade through each day, even when using this Norton product.  What is a realistic expectation?

thanks

jeff