Mail Transfer Agents: Add EmailRelay (#3599)

The EmailRelay is small enough for OpenWrt 16mb routers and much easier to configure than Postfix.
This makes it very useful for a self hosting.
It also works on Windows

Co-authored-by: nodiscc <nodiscc@gmail.com>

README.md

@@ -427,6 +427,7 @@ Simple deployment of [E-mail](https://en.wikipedia.org/wiki/Email) servers, e.g.
 - [chasquid](https://blitiri.com.ar/p/chasquid/) - SMTP (email) server with a focus on simplicity, security, and ease of operation. ([Source Code](https://blitiri.com.ar/git/r/chasquid/)) `Apache-2.0` `Go`
 - [Courier MTA](https://www.courier-mta.org/) - Fast, scalable, enterprise mail/groupware server providing ESMTP, IMAP, POP3, webmail, mailing list, basic web-based calendaring and scheduling services. ([Source Code](https://www.courier-mta.org/repo.html)) `GPL-3.0` `C`
 - [DragonFly](https://github.com/corecode/dma) - A small MTA for home and office use. Works on Linux and FreeBSD. `BSD` `C`
+- [EmailRelay](https://emailrelay.sourceforge.net/) - A small and easy to configure SMTP and POP3 server for Windows and Linux. ([Source Code](https://sourceforge.net/p/emailrelay/code/HEAD/tree/)) `GPL-3.0` `C++`
 - [Exim](https://www.exim.org/) - Message transfer agent (MTA) developed at the University of Cambridge. ([Source Code](https://git.exim.org/exim.git)) `GPL-3.0` `C`
 - [Haraka](https://haraka.github.io/) - High-performance, pluginable SMTP server written in Javascript. ([Source Code](https://github.com/haraka/Haraka)) `MIT` `Nodejs`
 - [MailCatcher](https://mailcatcher.me/) - Ruby gem that deploys a simply SMTP MTA gateway that accepts all mail and displays in web interface. Useful for debugging or development. ([Source Code](https://github.com/sj26/mailcatcher)) `MIT` `Ruby`