Maildir configuration
=====================

See <MailboxFormat.Maildir.txt> for a complete description of how Dovecot has
implemented Maildir support.

Mail location
-------------

Maildir exists almost always in '~/Maildir' directory. The mail location is
specified with:

---%<-------------------------------------------------------------------------
mail_location = maildir:~/Maildir
---%<-------------------------------------------------------------------------

Directory layout
----------------

By default Dovecot uses Maildir++ directory layout. This means that all
mailboxes are stored in a single directory and prefixed with a dot. For
example:

 * Maildir/.folder/
 * Maildir/.folder.subfolder/

If you want maildirs to use hierarchical directories, such as:

 * Maildir/folder/
 * Maildir/folder/subfolder/

you'll need to enable fs layout:

---%<-------------------------------------------------------------------------
mail_location = maildir:~/Maildir:LAYOUT=fs
---%<-------------------------------------------------------------------------

Control files
-------------

Dovecot stores some Maildir metadata into two control files:

 * 'dovecot-uidlist' file contains IMAP UID <-> Maildir filename mapping
 * 'dovecot-keywords' file contains Maildir filename flag (a..z = 0..25) <->
   keyword name mapping

Both of these files are described fully in <MailboxFormat.Maildir.txt>. The
important thing to remember about them however is that they shouldn't be
treated the same way as index files. Index files can be deleted and rebuilt
without any side effects, but if you delete control files you'll cause messages
to get new UIDs and possibly lose keyword names.

If the messages get new UIDs, the IMAP clients will invalidate their local
cache and download the messages all over again. If you do this for all the
users, you could cause huge disk I/O bursts to your server.

Dovecot can't currently handle not being able to write the control files, so it
will cause problems with <filesystem quota> [Quota.FS.txt]. To avoid problems
with this, you should place control files into a partition where quota isn't
checked. You can specify this by adding ':CONTROL=<path>' to 'mail_location',
for example:

---%<-------------------------------------------------------------------------
mail_location = maildir:~/Maildir:CONTROL=/var/no-quota/%u
---%<-------------------------------------------------------------------------

Index files
-----------

See <MailLocation#indexfiles> [MailLocation.txt] for full explanation of how to
change the index path. For example:

---%<-------------------------------------------------------------------------
mail_location = maildir:~/Maildir:INDEX=/var/indexes/%u
---%<-------------------------------------------------------------------------

Optimizations
-------------

 * 'maildir_very_dirty_syncs=yes': Assume that only Dovecot accesses 'cur/'
   directory. If another process (or even Dovecot which doesn't update index
   files) does changes to 'cur/' while the mailbox is simultaneously being
   modified by Dovecot, Dovecot may not notice those external changes. It's
   still safe to deliver new mails to 'new/' using non-Dovecot software (except
   with 'mailbox_list_index=yes' changes aren't noticed outside INBOX).
 * 'maildir_copy_with_hardlinks=yes' (default): When copying a message, do it
   with hard links whenever possible. This makes the performance much better,
   and it's unlikely to have any side effects. Only reason to disable this is
   if you're using a filesystem where hard links are slow (e.g. HFS+).
 * 'maildir_stat_dirs=no' (default): Assume that all the files beginning with a
   dot in the maildir are maildirs. You shouldn't have any non-directory files
   beginning with a dot in the maildirs, but if you do you may need to set this
   to "yes", in which case Dovecot needs to stat() each directory entry, which
   degrades the performance. Some filesystems provide the
   directory/non-directory status for free without having to stat(). In those
   filesystems this setting is ignored.

Filesystem optimizations
------------------------

See <MailboxFormat/Maildir#Maildir_and_filesystems>
[MailboxFormat.Maildir.txt].

Mailbox directory name
----------------------

When using 'LAYOUT=fs', there is a potential for naming collisions between
Maildir's 'new/', 'cur/' and 'tmp/' subdirectories, and mail folders of the
same names. For example, consider a mail folder "foo/bar". Under 'LAYOUT=fs',
data for this mail folder will be stored at under Maildir's usual three
directories '~/Maildir/foo/bar/{new,cur,tmp}/'.

If the user then tries to create a mail folder "foo/bar/new", this would then
imply that data should be stored in Maildir's three directories
'~/Maildir/foo/bar/new/{new,cur,tmp}/'. But this would overlap Maildir's 'new/'
subdirectory of mail folder "foo/bar".

This may not be a problem in many installations, but if a risk of collisions
with Maildir's three subdirectory names is perceived, then the 'DIRNAME'
parameter can be used. For example, if we specify mail location as:

---%<-------------------------------------------------------------------------
mail_location = maildir:~/Maildir:LAYOUT=fs:DIRNAME=mAildir
---%<-------------------------------------------------------------------------

then this will push Maildir's 'new/', 'cur/' and 'tmp/' subdirectories down
into a subdirectory 'mAildir/', so a mail folder "foo/bar" would be stored at
'~/Maildir/foo/bar/mAildir/{new,cur,tmp}/'. A mail folder "foo/bar/new" would
be stored at '~/Maildir/foo/bar/new/mAildir/{new,cur,tmp}/', which would then
have no overlap with the mail folder "foo/bar".

'DIRNAME' affects INBOX slightly differently. Without 'DIRNAME', INBOX will be
stored at '~/Maildir/{new,cur,tmp}/', but when 'DIRNAME' is specified, we get
an extra path component 'INBOX/' immediately prior to the 'DIRNAME' value, so
in the example above INBOX would be stored at
'~/Maildir/INBOX/mAildir/{new,cur,tmp}/'.

The value for 'DIRNAME' should be chosen carefully so as to minimise the
chances of clashing with mail folder names. In the example here, unusual
upper/lower casing has been used.

(This file was created from the wiki on 2017-10-10 04:42)