SmarterMail
Powerful mail client, focusing on simplicity and comfort
IceWarp Server
IceWarp Server is an all-in-one secure messaging and collaboration server platform designed to meet the needs of businesses of any size.
smtp4dev
smtp4dev is a free, open-source program that provides a fake SMTP server for testing and development purposes.
hMailServer
An efficient alternative to your typical windows email server that's free and private
XMail
An email server used on windows that can reach the intranet