MIX is a high-performance, indexed, on-disk email storage system that is designed for use with the IMAP protocol.
The MIX format was designed with an emphasis on very high scalability, reliability, and performance, while efficiently supporting modern features of the IMAP protocol.
Thus a directory with gigabytes of mail in it may appear to be empty if examined with tools that don't show hidden files.
[citation needed] By design, it is possible to recover the mailbox into a usable state if any of these files is lost or corrupted.
In addition, each status file entry also has a modification sequence, which permits lossless synchronization of multiple consumer message flag/keyword updates/ MIX allows for implementation-specific extensions.
Unlike maildir, however, MIX supports an index file for fast opens and mailbox scanning.
A MIX directory will tend to have a smaller number of files than a corresponding maildir mailbox as a result, which can be advantageous on certain operating systems.
Like maildir, and unlike mbox, MIX supports mail boxes that contain both messages and subordinate mailboxes.
MIX supports multiple clients concurrently reading and writing to individual mailboxes, which can not be achieved with mbox.