Winmail Mail Server 

Winmail Server is an enterprise class mail server software system offering a robust feature set, including extensive security measures. Winmail Server supports SMTP, POP3, IMAP, Webmail, LDAP, multiple domains, SMTP authentication, spam protection
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AXIGEN Mail Server 

AXIGEN is fast, reliable and secure mail server on Linux, offering (E)SMTP, POP3, IMAP4 and WEBmail services, with centalised Web/CLI Admin and FREE support included, enabling the System Administrator to have full control of the email traffic.
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NetMail-Light 

NetMail is a mail system for local networks and mobile access, either with the built-in webmail interface, or using NetMail's own client software. Also optimized for GSM, GPRS, UMTS, TCP/IP connections. (Not suited for Outlook as client.)
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