Do you receive many emails and want to answer them with a team of agents?
You're going to love Zammad!
Zammad is a web based open source helpdesk/customer support system with many features to manage customer communication via several channels like telephone, facebook, twitter, chat and emails. It is distributed under version 3 of the GNU AFFERO General Public License (GNU AGPLv3).
The code is open source, and available on GitHub!