A mail server is the computerized equivalent of your friendly neighborhood mailman. Every email that is sent passes through a series of mail servers along its way to its intended recipient. Although it may seem like a message is sent instantly – zipping from one PC to another in the blink of an eye – the reality is that a complex series of transfers takes place. Without this series of mail servers, you would only be able to send emails to people whose email address domains matched your own – i.e., you could only send messages from one example.com account to another example.com account.
Zimbra provides open-source server and client software for numerous applications like messaging and collaboration: email, group calendaring, contacts, and web document management and authoring.
The Zimbra server has been made available for various platforms like Linux, Mac OS X, appliances, and virtualization platforms. The Zimbra Web 2.0 Ajax client runs on most commonly used browsers like Firefox, Safari, and IE. It also features easy integration/mash-ups of web portals, business applications, and VoIP using web services.
When it comes to comparison between Zimbra and Microsoft Exchange, Zimbra is in par with Exchange in many ways. It is in fact ahead of Exchange for hosting providers and in collaboration features. One of the notable differences between Zimbra and Exchange is that Zimbra provides SOAP bindings which allow third parties to integrate additional functionality with Zimbra.
Advantages of Zimbra Mail Server
- Zimbra has equally rich or better features compared to Exchange.
- User Interface is very intuitive
- Year on year cost savings are phenomenal
- It can also work in an environment where the server is on Linux and the desktops on Mac or Windows
- Zimbra has a SaaS/Hosted model that keeps administration headaches away
- Zimbra is a clear winner! – especially for the SME segment
For more refer this doc
Postfix is an efficient and feature-rich mail server that was designed by Wietse Venema at the IBM T.J. Watson Research Center. It was intended to be a replacement for the popular sendmail. While Sendmail was the most popular mail server for many years, Postfix popularity has likely grown beyond that of Sendmail, due to its simple configuration, historically secure implementation, and high performance architecture. Also, because Postfix is designed to behave outwardly like sendmail, it is a mostly drop-in replacement for the older, larger, and slower mail server. It does lack some of the obscure features of sendmail, but the features it lacks are rarely used by the vast majority of users, so they are not often missed. And, it has some additional features of its own, not found in other mail servers.
Exim is a mail transfer agent (MTA) used on Unix-like operating systems. Exim is free software distributed under the terms of the GNU General Public License, and it aims to be a general and flexible mailer with extensive facilities for checking incoming e-mail.
Exim 4 has been ported to most Unix-like systems, as well as to Microsoft Windows using the Cygwin emulation layer. Exim is currently the default MTA on Debian GNU/Linux systems.
A large number of Exim installations exist, especially within Internet service providers and universities in the UK. Exim is also widely used with the GNU Mailman mailing list manager, and cPanel.