The Maildir e-mail format is a common way of storing email messages on a file system, rather than in a database. Each message is assigned a file with a unique name, and each mail folder is a file system directory containing these files. Maildir was designed by Daniel J. Bernstein circa 1995, with a major goal of eliminating the need for program code to handle file locking and unlocking through use of the local filesystem.

  • The <code>tmp</code> subdirectory temporarily stores e-mail messages that are in the process of being delivered. This subdirectory may also store other kinds of temporary files.
  • The <code>new</code> subdirectory stores messages that have been delivered, but have not yet been seen by any mail application.
  • The <code>cur</code> subdirectory stores messages that have already been seen by mail applications. offers flag synchronization in addition to arbitrary user-defined flags, while Dovecot uses lowercase letters to match 26 IMAP keywords,

Systems that don't allow colons in filenames (this includes Microsoft Windows and some configurations of Novell Storage Services) can use a non-standard alternative separator, such as ";" or "-". It is often trivial to patch free and open-source software to use a different separator. (efficient and extensible email client)

  • Balsa previously the official GNOME mail reader (prior to Evolution)
  • Cone a curses-based mail reader
  • Evolution, official GNOME mail client
  • GNUMail
  • Gnus
  • KMail, KDE mail reader
  • mailx
  • Mutt
  • Notmuch (fast, global-search and tag-based email system)
  • Pine/Alpine
  • Mozilla Thunderbird – experimental and “disabled by default because there are still many bugs”

Notes and references

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See also

  • mbox
  • MH Message Handling System
  • MIX (email)
  • manual page for maildir
  • maildir specifications