SpamDummy! 

SpamDummy! is a powerful and easy to use spam blocker for all POP3 email clients. SpamDummy! blocks spam, email viruses, and harmful content directly at the email server so that you never waste time downloading them.
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BusinessMail Email Server + Anti Spam System 

Fully multi threaded email server and anti-spam system with POP/SMTP plus web interface, offering powerful fully asynchronous operations, fully user configurable anti-spam system, user configurable filtering, aliasing, list handling plus lots more.
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CapeSoft Email Server 

Email Server with free upgrades and unlimited users for $30. For small or medium businesses and home environments. Is easy to use and provides you with full control over email domains, mailboxes and aliases.
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DNS2Go 

DNS2Go is a service for those seeking to leverage the true potential of their computer and Internet connection. Host your own website. Host an FTP server. Host your own email server and provide your family with a highly personalized email address.
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Officium Business Server 

Officium Business Server is a revolutionary web-based office collaboration server that boasts 20 powerful business tools including a full blown email server and 100% compatible MS Office suite of tools.
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MDaemon 

MDaemon , Windows-based email server software, contains full mail server functionality and control with a strong emphasis on security to protect your email communication needs. Security features include Greylisting, DKIM, DomainKeys (DK), and SPF.
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