Microsoft Exchange and its associated Outlook client have been the face of enterprise communications for many years and are pretty much synonymous with the idea of work email. That does not mean, however, that there are not open source alternatives. There is a slate of clients/email servers that replicate the functions of Microsoft’s email solutions and not only have transparent code but plug into Linux server backends. One of the most well-known is Zarafa.
Zarafa released its email client/server technology as open source in 2008. Its distinguishing feature is that it is offered as a full-fledged, transparent replacement for Exchange, giving all its benefits as well as some additional features not available on the proprietary system:
Zarafa has maintained an almost identical look and feel compared to Outlook, which is good news for any organization that decides to switch over as users can easily adjust. It not only is familiar in layout but carries similar features such as the address book, calendar, and public folders to which Outlook users have become accustomed. It also provides connectivity with Outlook by means of a plugin. Microsoft uses the proprietary Messaging API (MAPI) for communication between Exchange and Outlook. Zafara has implemented its own version (Mapi4Linux) for compatibility. Like Exchange it can also perform authentication through LDAP and Active Directory.
Linux is the platform of choice for Zafara, as you would expect, and it plugs into a MySQL database for added security. In addition to the difference in OS, the email client for Zafara is an AJAX-based web-app as opposed to being a stand-alone application like Outlook, giving it high accessibility as well as ease of use from mobile devices. As with all open-source solutions, it is cheaper than Exchange to license but not entirely free, as it comes in Standard, Professional, and Enterprise editions at different price points.