Dovecot2.3.21.1

Dovecot is an open source IMAP and POP3 server for Linux/UNIX-like systems, written with security primarily in mind. Although it's 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 it's fully compatible with UW-IMAP and Courier IMAP servers' implementation of them, as well as mail clients accessing the mailboxes directly. It's easy to migrate from them to Dovecot. Dovecot will also soon have its own high performance mailbox format called dbox. Perhaps some day in future Dovecot will also support storing mails in SQL databases.

Dovecot is easy to set up and doesn't require special maintenance. The only thing you need is to get the authentication working properly, and if your users are in /etc/passwd, there's 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 of the 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 a mailbox, Dovecot can get most of the wanted information from its indexes with little effort. Dovecot's indexes can scale to a huge amount of messages per mailbox without hardly any noticeable slowdown. I've tested only up to 367000 mails, but even millions of messages shouldn't be a problem.

Dovecot has very small memory needs. Most of it goes to mmap()ed index files, which means that if operating system is low on memory, it can simply drop those memory pages without having to move them to swap. Connections are handled in separate processes, each one currently using around 100kB of swappable memory. Some extensions such as SORT and THREAD require more memory to work though.

Dovecot is fail safe. Indexes could be potentially 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 a crash is considered a bug and will be fixed, even if it happens only by deliberately poking the index files.