TekSMTP is a simple SMTP/POP3 server runs under Windows (XP, Vista, Windows 7/8, 2003/2008/2012 Server). TekSMTP consists of a GUI (TekSMTP Manager) and a service application. Major features; Simple design and easy to use user interface, Simple interface for user definitions, Multi domain operation, TLS support for both POP3 and SMTP, Customizable SMTP ports, Black listing and RBL for anti-spam, POP3 password discovery for migration, Performance monitoring through Windows Performance Monitor. TekSMTP can query RBL databases to filter SPAM messages. You can specify your own DNS black lists. Some RBL systems require connecting them directly. You can also check validity of sender domain.