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At present (Fall 1999) system administrators have the choice between
three different (more or less free) solutions when having to set up
an IMAP server.
- UW
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UW IMAP
(IMAP server of University of Washington) has been the "standard"
IMAP server on many Unix systems for a long time. It is simple to
install and use and works great with any mail system using the
traditional mbox format such as sendmail.
However, the list of bugs and exploits has grown quite long over the
last couple of years. This fact and the need for additional features,
which UW does not provide, made people looking for alternatives.
- Cyrus
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CMU Cyrus
has been designed to handle massive quantities of mail, which is
often the case at ISP's. Another interesting feature, which often
makes it the number one choice at ISP's is Cyrus' detached user database:
users do not need accounts on the hosts running Cyrus. The server
keeps both, user information and and mail messages, in a separate
part of the file system, which is only accessible by the IMAP server.
All access to the data has to go through and authorized by the daemon.
This makes Cyrus interesting for sites with lots of users and large
amounts of traffic. However, Carnegie Mellon University's license
restricts Cyrus IMAP from being true free software. CMU also implemented
the SASL (Simple Authentication and Security Layer) library, which is
used nowadays by many other mail and network servers for authentification
purposes.
- Courier
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Courier
is a new IMAP server exclusively working on the Maildir format provided
by Qmail, Exim
and Postfix. It does not support traditional
mbox files. Courier includes an additional POP3 server. It supports abstract
authentication modules like PAM, LDAP and even MySQL. If OpenSSL is
installed on the system Courier provides secure connections using IMAP
over SSL. Courier is said to be the new shooting star in the sky of
IMAP servers.
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