Ninja Email Security Appliance from Sunbelt Software is almost like an email security plugin for Microsoft Exchange servers.

Ninja Email Security is both easy to install and simple to manage. Installation takes place directly on the Exchange server and is guided by a short setup wizard.
After the initial configuration is complete further tweaking and management is done using the Ninja Console. This console is clean and well organised with tab navigation.
We found this product to plug in so nicely with our Exchange server, we almost thought it was part of Exchange. It also has the flexibility to plug into Exchange 2000, 2003, or 2007, which means the existing environment can stay intact, with no need for upgrading.
Ninja can pull users and groups straight from Active Directory, so policy can be assigned using the already defined structure. Policy and settings are also quite easy to manage and most take just a few clicks of the mouse.
There are two documents provided with the Ninja software. The quick-start guide nicely outlines pre-installation, installation and post-installation processes. The user manual goes into further depth on the same three areas. This guide also includes many screenshots and step-by-step instructions.
Sunbelt offers office-hour email and phone support at no cost to customers for one year. Additional 24/7 support can be purchased for a fee of 25 per cent of the purchase price. Other assistance on offer includes a support area on the website with a knowledge base, FAQs and technical documentation.
At a price of just £318 for 25 mailboxes, we find this product to be average value for money. While it does have some great features, it can become pricey very quick for larger environments.