Did you know with open source software you get open API? Meaning you have the ability to talk to the software and have control over how you talk to the software through open protocols. Zimbra explains the difference between open and closed API. https://www.zimbra.com/

Zimbra is all about security and data privacy. Our open platform implements deep security features as well as integrations with the most popular 3rd party security applications. In addition, Zimbra has scalable deployment options ensuring complete privacy for organizations from mid-sized service provider to large telecoms.