Outlook Spam Filter Review Overall Rating:

Description

As the name would suggest, Outlook Spam Filter is an Outlook plug-in. It is a Bayesian filter, with whitelist/blacklist functionality and rudimentary content-based filtering.

Verdict

Outlook Spam Filter took a while to "settle down" and start returning decent capture rates, but in the end proved quite good at correctly identifying messages. Others have been more accurate, but good results nonetheless.

Nice clean interface with the minimum of interaction required by the user.

Installation

Installation went smoothly. During installation, it scans your sent items folder to "learn" what constitutes a good message.

Outlook Spam Filter's web site states that the filter is "pre-trained" from more than 30,000 spam letters, so should be working well from installation.

Interface

Familiar to previous users of Outlook add-in spam filters, Outlook Spam Filter adds its toolbar to the Outlook Interface:

The only other interface element that the user will occasionally need to interact with is the settings dialog, which presents a clear and intuitive interface:

Features and Operation

One of the big advantages to Bayesian-based filters is the lack of interaction required in daily use. It is mostly a simple case of using two buttons to correct wrongly identified messages (In this case by clicking either the "Add to Friends" or "Add to Enemies" buttons on the main toolbar).

In this case however, we did find a minor annoyance: whenever you click the "Add to Enemies" button, such as when a spam message makes it through to the inbox, you are presented (every time) with the following dialog:

Both of these questions would be better moved to an option in the settings dialog. The answer to both of these questions would most almost certainly be the same every time it is answered, but this dialog popped up every time.
We even tried to disable the enemies list in the settings dialog, but this just earned us an extra option in the message box asking us if we would like to enable it again! No big deal maybe, but we did find this getting on our nerves somewhat (maybe too much coffee and too little sleep?)

Aside from the Bayesian filtering, which is the main heart of Outlook Spam Filter, there is some rudimentary content-based filtering. Messages can be flagged as spam on certain header conditions and there is the ability to add some "Spam Recognition Keywords".

These are simple text only matches so will add little to the capture rate of the filter.

A click on the "Bounce" button and a forged undeliverable message will be sent to the sender of the currently selected message.

Accuracy

During our week-long test of Outlook Spam Filter, we noticed a definite increase in accuracy as it "learned" from the messages that were received.
We definitely didn't get the 97% accuracy that their web site promises "out of the box", but things did improve the longer the test went on.

Unusually, we had more false positives than false negatives which prompted us to pay more attention to searching the spam folder for incorrectly identified messages.

In the end, the accuracy returned was 93.61%. Not as good as we would have liked, but we feel this would definitely have improved with time.

Conclusion

Outlook Spam Filter proved itself to be a stable and simple to use solution.

The overall average accuracy returned from our tests was not as good as similar filters we have tested, but it has to be considered that Bayesian filters only reach optimum accuracy after as much as a month of continuous use. We could see it improving toward the end of our tests.

Because of this accuracy figure though, it didn't quite make our 5 star rating.

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