Mailboxes with this extension are file directories. Each Mailbox message is stored as a separate file in the Mailbox directory.
The message file name has the following format:iiii_O_oooo-flags-timestamp-nLines_where iiii is the message unique ID, O_oooo is the message permanent UID (optional), flags are the message status flags, the timestamp is the message internal time stamp - the time (GMT) when the message was added to the Mailbox, in the <tt style="font-size: 13px; color: rgb(0, 0, 0); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;">yyyymmddhhmmss</tt> format, and nLines is the number of text lines in the message.
**Note:**On the Unix platforms, the MailDir Mailboxes implement the shared storage model: if the same message is directed to many Accounts/Mailboxes, only one message file is created, and a hard link to that file is placed into each Mailbox directory. When a message is removed from all Mailboxes, the file is automatically deleted by the OS. This feature is disabled for the Accounts that have the Erase Deleted Messages Setting enabled.
To store Message Attributes, special files with O_oooo_ names are created inside the Mailbox directory.
Note: most freeware mail systems use either the mbox-like or mdir-like formats, and designers of those systems make various claims about the advantages of the formats they have selected. It is important to remember that:
Note: the Text format is more efficient than the MailDir format in most cases, this is why this format is used as the default one. The MailDir format is recommended only for those Mailboxes that contain many (100 or more) large (1MB or more) messages. If a user has a Proposals Mailbox where she stores all messages with attached documents, each 0.5-5MB in size, then this Mailbox may work faster if it is created in the .mdir format.