dovecot included dovecot-mruby-plugin is a programmable IMAP/POP server scripting with mruby like ngx_mruby for nginx, mod_mruby for apache httpd and trusterd for HTTP/2 mruby Web server. Also pmilter is a programmable Milter server scripting with mruby for SMTP server like IMAP command register and pre or post command hook using mruby.
Pmilter is a smple and programmable mail filter server software. You can control smtp server like postfix or sendmail via some mruby scripts. Pmilter is one-binary. So you can deploy and setup environment very easily. Enjoy!!
STNS use JSON API via HTTP protocol. So STNS server can place under a http reverse proxy like nginx. It's very useful when used in combination with other servers.