Dovecot 1.0.2 / 1.1 Alpha 3

Dovecot project is an open source POP3 and IMAP server for Linux/UNIX-like systems, written with security primarily in mind. Although its written in C, it uses several coding techniques to avoid most of the common pitfalls.
Dovecot can work with standard mbox and maildir formats and its fully compatible with UW-IMAP and Courier IMAP servers implementation of them as well as mail clients accessing the mailboxes directly.
Its easy to migrate from them to Dovecot. I have also plans to support storing mails in SQL databases.
Dovecot is easy to set up and doesnt require special maintenance. Only thing you need is to get the authentication working properly - if your users are in /etc/passwd theres hardly anything you have to do.
Dovecot should be pretty fast. There are still some optimizations that could be done, but I believe it already beats most other IMAP servers in overall performance.
This is mostly because of index files that Dovecot maintains; instead of having to scan through all the data in mailbox, Dovecot can get most of the wanted information from index with little effort.
Dovecots indexes can scale to huge amount of messages per mailbox with hardly any noticeable slowdown. Ive tested only up to 367000 mails, but millions of messages should be no problem.
Dovecot takes very little memory. Most of it goes to mmap()ed index and mailbox files, meaning that if operating system is low on memory, it can simply drop those memory pages without having to store them in swap.
Connections are handled in separate processes, each one currently using around 100kB of swappable memory. Some extensions like SORT and THREAD will require more memory to work though.
Dovecot is fail safe. Indexes could potentially be quite a large problem maker, but Dovecot does sanity checks to all data before using it to avoid crashes and other problems.
Any kind of crash is considered as bug and will be fixed - even if it happens only by deliberately poking the index files.
Main features:
- Dovecot should be quite ready for use with normal IMAP clients.
- Complete IMAP4rev1 support.
- Supports THREAD and SORT extensions, required by many IMAP webmails.
- Complete TLS/SSL support
- IPv6 ready.
- Shared mailboxes arent yet supported.
- Maildir++ quota isnt yet supported. Hard filesystem quota can also be problematic.