This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.


A high performance mbox-replacement created by Mark Crispin while at University of Washington for UW-IMAP. Each message in the file is preceded by a record carrying all the metadata that IMAP-protocol needs. This allows changing the metadata easily by modifying the fixed-size header, rather than moving data around in a file like with mbox.

File locking is handled more intelligently (only appends may need to wait for locks), making this format a good choice for shared mailboxes.

Downsides contain:

MailboxFormat/mbx (last edited 2010-06-15 15:19:07 by TimoSirainen)