This product is available as Windows software, which we reviewed, or a dedicated Linux appliance. A combination of email content filtering and anti-spam technology, Message Inspector offers a comprehensive company-wide email security solution.

Minimum system requirements hint at the size and complexity of the package – an 800MHz processor and 1GB RAM (2GB is recommended).

As with most of the products on review in this test, Message Inspector combines a number of different detection methods. Over 2,500 attributes are scanned as part of its battle against the newer, more complex instances of spam. This is combined with the usual white- and blacklist method, which ZixCorp refers to as its Always Spam and Never Spam lists. The company's signature database is updated daily.

One of the software's most powerful aspects is its text-scanning, which can be configured to detect inappropriate content of both incoming and outgoing mail. This is pre-populated by default, but it's also fully customizable so we could configure it to our specific needs.

One potential downfall was that ZixCorp advises you to install on a dedicated machine, meaning that other technologies such as anti-virus and firewalls can't co-exist – unless you are running ZixCorp anti-virus, that is. ZixCorp has partnered with Sophos to provide the virus-scanning technology. The ZixCorp-badged Sophos virus engine sits on the gateway. A full quarantine management system is included to ensure that questionable email can be re-evaluated.

User groups can be imported from any LDAP database, and the product is fully hierarchical so different rules can be applied to users depending on risk levels. Several ZixCorp servers can be managed from a central console.

MI performed extremely well, with very little spam slipping through. Although we recorded the odd false positive, these were quarantined and no harm was done.