Webmail / IMAPS software for end-user clients in 2016

[eric.kuhnke at gmail.com (Eric Kuhnke)]

If you had to put up a public facing webmail interface for people to use,
and maintain it for the foreseeable future (5-6 years), what would you use?

Roundcube?
https://roundcube.net/

Rainloop?
http://www.rainloop.net/

Something else?


Requirements:
Needs to be open souce and GPL, BSD or Apache licensed

Email storage will be accessed via IMAP/TLS1.2

Runs on a Debian based platform with apache2 or nginx

Desktop browser CSS and mobile device CSS/HTML functionality on 4" to 7"
size screens with Chrome and Safari