hMailServer is a small, GPL-licensed email server for Windows that’s been around for over 20 years. Despite a couple of contributors continuing to offer sporadic updates and fixes, the lead developer no longer has the bandwidth to maintain it, so it's slowly dying. Despite its age and Windows-centric design, there’s potential for a revamp and a port to Linux.
hMailServer stands out as feature-rich, lightweight (just 4.2MB to download), and easy to set up and manage. Given Thunderbird’s integration of K-9 to expand into Android clients, perhaps adding an email server to the portfolio could be a strategic move. hMailServer could be an excellent fit. It can be found here: https://www.hmailserver.com/download
... View more