CheckYourNetwork.net - Online Domain Reputation Checking Tools

Senderbase.org - Senderbase.org

    SenderBase.org is the world's largest email and Web traffic monitoring network. First introduced in February 2003 IronPort's SenderBase Network collects nowadays data on more than 25 percent of the world's email traffic and provides an unprecedented real-time view into security threats from around the world. SenderBase can be used like a "credit reporting service" for email, providing comprehensive data that ISPs and companies can use to differentiate legitimate senders from spammers and other attackers and giving email administrators visibility into who is sending them email.
ReputationAuthority.org - ReputationAuthority.org
    BorderWare ReputationAuthority is the world’s most effective first line of defense reputation service for email and Web security. It stands alone for protecting enterprises as the first and only third-generation, zero-hour global monitoring and protection system purposely created for business and government. BorderWare ReputationAuthority proactively and automatically prevents unwanted email and Web-based spam, malware, and network threats from entering your network, resulting in a 98.3% block-rate being rejected at the connection-level.
Senderscore.org - Senderscore.org
    SenderScore.org provides you with access to detailed reputation reports and other free tools to improve the overall email experience for everyone, and promote transparency and trust between legitimate email senders and Internet Service Providers.
barracudacentral.org - barracudacentral.org
    BarracudaCentral.org, is devoted to sharing information with Barracuda Networks customers and the Internet security community. Here you will find a wide range of statistics, threat information, and a number of useful services to help manage and secure your network.

Be Sure to Check out Clustered Networks Untangle Security Appliances

The Untangle Gateway, the world's first commercial-grade open source solution for blocking spam, spyware, viruses, adware and unwanted content on the network, provides a free and better alternative to costly, inflexible proprietary appliances. Untangle's applications are currently being used in tens of thousands of businesses in a variety of industries, including financial services, real estate, education, bio-science, and professional services.