Some notes and pitfalls to install it, not sure it will become an official module for some reasons
- The upgrade path is a nightmare of mysqldb : https://www.mailpiler.org/wiki/current:upgrade
- Piler is smtp server itself it cannot be installed with a postfix server, piler must use the default smtp port, you need to make a Bcc inside your email server to send all emails to Piler, else you use pilerimport to read an imap account on your server.
- Sphinx is needed, V2 is supported, but now it is V3.3 and only binaries are provided, no rpm/deb for linux. I think it could be hard, when you start with a version all the sphinx indexes must be built again with a version change: https://www.mailpiler.org/wiki/current:sphinx3
- rh-php73-php-fpm is needed with a virtualhost : nethserver-rh-php73-php-fpm
- xlhtml need to be compiled or installed from the lux repository : http://repo.iotti.biz/CentOS/7/x86_64/xlhtml-0.5-19.el7.lux.x86_64.rpm
- we need a mysql database nethserver-mysql
- some optional rpms must be installed along : catdoc poppler poppler-utils unrtf tnef memcached libpst libzip tre
- The rpm of piler itself is not compatible with centos7 it expects that a group php-fpm exists to execute a post-install scrip : groupadd php-fpm
It is a software a bit tricky 
however there is not much alternative except mailArchiva but it is a paid software
Other idea could be to use it inside a docker container