Open source solutions in the email server space tend to comprise combinations of open source projects. This is because comprehensive solutions such as Microsoft Exchange and Novell GroupWise have set the expectation of a single email system that takes care of all the enterprise’s email serving needs, or at least those of a department within an enterprise. The open source community’s answer to this challenge is to combine several open source projects that work well together.
Open source email server software provides a low-overhead way to manage large volumes of mail. With appropriate staff expertise, open source-based email server solutions can also reduce an IT group’s exposure to the perils of spam and viruses.
It is instructive to look at Microsoft Exchange’s capabilities, because Microsoft Exchange offers a feature set that meets most of an enterprise’s common email requirements. We purposefully underemphasize collaboration features here since we address collaboration as a separate topic in Appendix D. Here is Microsoft Exchange’s feature set:
Full support for major email protocols like SMTP, POP3, IMAP, and WebDAV
Active Directory integration with full support for global address lists across the enterprise
Outlook web access and a full-featured web mail client, with S/MIME support, desktop-application-style shortcuts, task lists, and an integrated spellchecker
Deep integration with Outlook 2003
Security features ...