Namespaces

Dovecot supports fully configurable, hierarchical namespaces, which can use different storage drivers.

Their original and primary purpose is to provide Namespace IMAP extension (RFC 2342) support, which allows giving IMAP clients hints about where to locate mailboxes and whether they're private, shared or public.

Dovecot namespaces can be used for several other purposes too:

• Changing the Hierarchy Separators
• Providing backwards compatibility when switching from another IMAP server
• Provides support for public shared mailboxes and user shared mailboxes mailboxes
• Allows having mails in multiple different locations with possibly different formats

These different locations and drivers are presented to the client as a single tree.

Each namespace has:

• prefix (usually empty or "INBOX.")
• namespace separator (usually '/' or '.')
• 0 or more folders

There must be one namespace where the case-insensitive folder named INBOX exists.

All visible namespaces must have the same separator.

Inside each namespace there is a list of folders, which form a sub-hierarchy.

Folder Names

Each folder has a name. In configuration files and log files Dovecot almost always uses the "virtual name", which uses the configured namespace's hierarchy separator as well as the namespace prefix. Depending on the used mailbox_list_layout setting the internal folder name may be different. The internal name is stored in databases (e.g. mailbox subscriptions), which allows changing the namespace prefix or separator without having to change the databases.

The folder names use UTF-8 character set internally. All folder names must be valid UTF-8. With mailbox_list_layout = fs and mailbox_list_layout = Maildir++ the folder names are stored in filesystem paths as mUTF-7 (see IMAP RFC 3501) mainly for legacy reasons. This can be changed with the mailbox_list_utf8 setting.

Folder Name Lengths

Folder name length restrictions:

• Maximum length of an individual folder name within a hierarchy is 255 bytes. For example with "a/b/c" hierarchy each of the a, b and c can be a maximum of 255 bytes.
• The maximum folder path length is 4096 bytes.

The maximum folder name lengths work correctly when folder names aren't stored in filesystem, i.e. mailbox_list_layout = index is used. Otherwise the OS adds its own limitations to path name lengths and the full 4096 bytes can't be used. With mailbox_list_layout = Maildir++ the path must fit to 254 bytes (due to OS limitations).

Parent Folders

A folder can have one or more parent folders that do not physically exist. These are presented with \NoSelect or \Nonexistent attribute. It's possible to try to avoid creating these by using the mailbox_list_drop_noselect setting (enabled by default).

Configuration

If the Dovecot configuration doesn't explicitly specify a namespace, the inbox namespace is created automatically.

Namespace configuration is defined within a dovecot configuration block with the format:

namespace <name> {
  [... namespace settings ...]
}

The namespace name is only used internally within configurations. It allows you to update an existing namespace - by repeating the namespace block and adding additional configuration settings - or allows userdb to override namespace settings for specific users, e.g.:

namespace/name/prefix=foo/

Example configuration for default namespace:

namespace inbox {
  separator = .
  prefix =
  inbox = yes
}

Settings

namespace

Default	[None]
Value	Named List Filter

Creates a new namespace to the list of namespaces. The filter name refers to the namespace_name setting.

Example:

namespace foo {
  [...]
}

namespace_alias_for

Default	[None]
Value	string

Refers to an alias namespace's namespace_name.

If multiple namespaces point to the same location, they should be marked as aliases against one primary namespace. This avoids duplicating work for some commands (listing the same mailbox multiple times).

Mail user variables can be used.

Note: Alias namespaces often have hidden=yes and list=no so they are not visible unless clients have specifically configured them, and they're typically used when migrating to a different namespace prefix for existing users.

Example:

namespace inbox {
  prefix =
  # ...
}
namespace alias {
  prefix = INBOX/
  alias_for = inbox
}

namespace_disabled

Default	no
Value	boolean

If yes, namespace is disabled and cannot be accessed by user in any way.

Useful when returned by a userdb lookup to easily configure per-user namespaces.

namespace_hidden

Default	no
Value	boolean

If yes, namespace will be hidden from IMAP NAMESPACE (RFC 2342) command.

namespace_ignore_on_failure

Default	no
Value	boolean

If namespace's storage initialization fails, by default the entire session will fail to start. If this is set, this namespace will be ignored instead.

namespace_inbox

Default	no
Value	boolean

If yes, this namespace will be considered the one holding the INBOX folder.

There can be only one namespace defined like this.

namespace_list

Default	yes
Value	string
Allowed Values	yesnochildren
See Also	namespace_hidden

Include this namespace in LIST output when listing its parent's folders.

Options:

Value	Description
children	Namespace prefix list listed only if it has child mailboxes.
no	Namespace and mailboxes not listed unless listing requests explicitly mailboxes under the namespace prefix.
yes	Namespace and mailboxes are always listed.

It is still possible to list the namespace's folders by explicitly asking for them. For example, if this setting is no, using LIST "" * with namespace prefix "lazy-expunge/" won't list it, but using LIST "" lazy-expunge/* lists all folders under it.

namespace_name

Default	[None]
Value	string

Name of the namespace. This is used only in configurations - it's not visible to user. The namespace filter refers to this setting.

namespace_order

Default	[None]
Value	unsigned integer

Sets display order in IMAP NAMESPACE (RFC 2342) command.

Namespaces are automatically numbered if this setting does not exist.

namespace_prefix

Default	[None]
Value	string

Specifies prefix for namespace.

INFO

Must end with namespace_separator.

Mail user variables can be used.

Example:

namespace {
  prefix = Shared/
  separator = /
}

namespace_separator

Default	"." for Maildir; "/" for other mbox formats
Value	string
See Also	Namespaces: Hierarchy Separators

Specifies the hierarchy separator for the namespace.

The separator is a single character, which can't then otherwise be used in folder names.

The commonly used separators are . and /, but other separators can be used as well. For example ^ is less likely to be found in normal folder names.

Recommended value is to leave it empty and accept the default value.

namespace_subscriptions

Default	yes
Value	boolean

Whether subscriptions are stored in this namespace.

This is usually no for shared namespaces so that the shared folders' subscriptions are stored in the user's primary subscriptions file. If no, the subscriptions are stored in the first parent namespace (based on the prefix) that has this setting enabled.

Example: If this setting is no for a namespace with prefix=foo/bar/, Dovecot first sees if there's a prefix=foo/ namespace with subscriptions=yes and then a namespace with an empty prefix. If neither is found, an error is given.

namespace_type

Default	private
Value	string
Allowed Values	privatesharedpublic

The namespace type. One of:

Type	Description
public	Contains public shared mailboxes.
private	Typically contains only user's own private mailboxes.
shared	Contains other users' user shared mailboxes.

Hierarchy Separators

namespace_separator specifies the character that is used to separate the parent mailbox from its child mailbox.

For example if you have a mailbox "foo" with child mailbox "bar", the full path to the child mailbox would be "foo/bar" with / as the separator, and "foo.bar" with . as the separator.

IMAP clients, Sieve scripts, and many parts of Dovecot configuration use the configured separator when referring to mailboxes. This means that if you change the separator, you may break things.

However, changing the separator doesn't change the on-disk "layout separator".

Example:

mailbox_list_layout	Layout Separator	Namespace Separator	Mailbox Name	Directory
Maildir++ (default)	.	.	foo.bar	~/Maildir/.foo.bar/
Maildir++ (default)	.	/	foo/bar	~/Maildir/.foo.bar/
fs	/	.	foo.bar	~/Maildir/foo/bar/
fs	/	/	foo/bar	~/Maildir/foo/bar/

TIP

The "namespace separator" changes only the "mailbox name", but doesn't change the directory where the mails are stored. The "layout separator" can only be changed by changing mailbox_list_layout, which also affects the entire directory structure.

The layout separator also restricts the mailbox names. For example if the layout separator is ., you can't just set separator to / and create a mailbox named foo.bar.

A commonly used separator is /. It probably causes the least amount of trouble with different IMAP clients. The ^ separator is troublesome with Thunderbird. If \ has to be used, it needs to be escaped in configuration:

namespace {
  separator = "\\"
}

You should use the same hierarchy separator for all namespaces. All list=yes namespaces must use the same separator, but if you find it necessary (e.g. for backwards compatibility namespaces) you may use different separators for list=no namespaces.

Values From userdb

To change namespace settings from userdb, you need to return namespace/<name>/setting+=value.

To create a namespace, make sure you first return namespace+=<name>[,<name>,...] and settings after this.

This adds a new given namespace. Without + all the namespaces are replaced with the given list.

userdb static {
  fields {
    namespace += special
    namespace/special/mail_path = /var/special/%{user}
    namespace/special/prefix = special/
  }
}

Shared Mailboxes

See shared mailboxes.

Examples

Mixed mbox and Maildir

If you have your INBOX as mbox in /var/mail/username and the rest of the mailboxes in Maildir format under ~/Maildir, you can do this by creating two namespaces:

namespace {
  separator = /
  prefix = "#mbox/"
  mail_driver = mbox
  mail_path = ~/mail
  mail_index_path = /var/mail/%{user}
  inbox = yes
  hidden = yes
  list = no
}

namespace {
  separator = /
  prefix =
  mail_driver = maildir
  mail_path = ~/Maildir
}

Without the list = no setting in the first namespace, clients would see the "#mbox" namespace as a non-selectable mailbox named "#mbox" but with child mailboxes (the mbox files in the "~/mail" directory), i.e. like a directory. So specifically with inbox = yes, having list = no is often desirable.

Backwards Compatibility: UW-IMAP

When switching from UW-IMAP and you don't want to give users full access to filesystem, you can create hidden namespaces which allow users to access their mails using their existing namespace settings in clients.

# default namespace
namespace inbox {
  separator = /
  prefix =
  inbox = yes
}

# for backwards compatibility:
namespace compat1 {
  separator = /
  prefix = mail/
  hidden = yes
  list = no
  alias_for = inbox
}
namespace compat2 {
  separator = /
  prefix = ~/mail/
  hidden = yes
  list = no
  alias_for = inbox
}
namespace compat3 {
 separator = /
 prefix = ~%{user}/mail/
 hidden = yes
 list = no
 alias_for = inbox
}

Backwards Compatibility: Courier IMAP

Recommended: You can continue using the same INBOX. namespace as Courier:

namespace inbox {
  separator = .
  prefix = INBOX.
  inbox = yes
}

Alternatively: Create the INBOX. as a compatibility name, so old clients can continue using it while new clients will use the empty prefix namespace:

namespace inbox {
  separator = /
  prefix =
  inbox = yes
}

namespace compat {
  separator = .
  prefix = INBOX.
  inbox = no
  hidden = yes
  list = no
  alias_for = inbox
}

The separator=/ allows the INBOX to have child mailboxes. Otherwise with separator=. it wouldn't be possible to know if "INBOX.foo" means INBOX's "foo" child or the root "foo" mailbox in "INBOX." compatibility namespace. With separator=/ the difference is clear with "INBOX/foo" vs. "INBOX.foo".

The alternative configuration is not recommended, as it may introduce issues:

• Although clients may do LIST INBOX.*, they may still do LSUB *, resulting in mixed results.
• If clients used empty namespace with Courier, they now see the mailboxes with different names, resulting in redownloading of all mails (except INBOX).
• Some clients may have random errors auto-detecting the proper default folders (Sent, Drafts etc) if the client settings refer to old paths while the server lists new paths.

See also migrating mailboxes

Per-user Namespace Location From SQL

You need to give the namespace a name, for example "docs" below:

namespace docs {
  type = public
  separator = /
  prefix = Public/
}

Then you have an SQL table like:

CREATE TABLE Namespaces (
  [...]
  Location varchar(255) NOT NULL,
  [...]
)

Now if you want to set the namespace location from the Namespaces table, use something like:

userdb sql {
  query = SELECT Location as 'namespace/docs/mail_path' \
    FROM Namespaces \
    WHERE ..
}

If you follow some advice to separate your "INBOX", "shared/" and "public/" namespaces by choosing "INBOX/" as your prefix for the inboxes you will see, that you run into troubles with subscriptions. Thats, because there is no parent namespace for "shared/" and "public/" if you set subscriptions = no for those namespaces.

If you set subscriptions = yes for "shared/" and "public/" you will see yourself in the situation, that all users share the same subscription files under the location of those mailboxes.

One good solution is, to create a so called "hidden subscription namespace" with subscriptions turned on and setting subscriptions = no for the other namespaces:

namespace subscriptions {
  subscriptions = yes
  prefix = ""
  list = no
  hidden = yes
}

namespace inbox {
  inbox = yes
  subscriptions = no

  prefix = INBOX/
  separator = /

  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }

  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }

  mailbox "Sent Messages" {
    special_use = \Sent
  }

  mailbox Spam {
    auto = subscribe
    special_use = \Junk
  }

  mailbox Trash {
    auto = subscribe
    special_use = \Trash
  }
}

namespace {
  type = shared
  prefix = shared/$user/
  mail_driver = mdbox
  mail_path = %{owner_home}/mdbox
  mail_index_private_path = %{owner_home}/mdbox/shared
  list = children
  subscriptions = no
}

namespace {
  type = public
  separator = /
  prefix = public/
  mail_driver = mdbox
  mail_path = /usr/local/mail/public/mdbox
  mail_index_private_path = ~/mdbox/public
  subscriptions = no
  list = children
}

Mailbox Settings

Mailbox configuration is typically defined inside a namespace block so it only applies to the specific namespace.

Settings

mailbox

Default	[None]
Value	Named List Filter

Create a new mailbox to the list of mailboxes. The filter name refers to the mailbox_name setting.

TIP

If the mailbox name has spaces, you can put it into quotes:

mailbox "Test Mailbox" {
  # ...
}

mailbox_auto

Default	no
Value	string
Allowed Values	createnosubscribe

Autocreate and/or subscribe to the mailbox?

Value	Description
create	Autocreate but don't autosubscribe
no	Don't autocreate or autosubscribe
subscribe	Autocreate and autosubscribe

Autocreated mailboxes are created lazily to disk only when accessed for the first time. The autosubscribed mailboxes aren't written to subscriptions file, unless SUBSCRIBE command is explicitly used for them.

mailbox_autoexpunge

Default	[None]
Value	time
See Also	mailbox_autoexpunge_max_mails

Expunge all mails in this mailbox whose saved-timestamp is older than this value.

For IMAP and POP3 this happens after the client is already disconnected.

For LMTP this happens when the user's mail delivery is finished. Note that in case there are multiple recipients, autoexpunging is done only for some of the recipients to prevent delays with the mail delivery: The last recipient user is autoexpunged first. Next, the first recipient user is autoexpunged (because the first user's mail was kept open in case it could be directly copied to the other users). None of the middle recipient users are autoexpunged.

mailbox_list_index = yes is highly recommended when using this setting, as it avoids actually opening the mailbox to see if anything needs to be expunged.

mail_always_cache_fields = date.save is also recommended when using this setting with sdbox or Maildir, as it avoids using stat() to find out the mail's saved-timestamp. With mdbox format this isn't necessary, since the saved-timestamp is always available.

mailbox_autoexpunge_max_mails

Default	[None]
Value	unsigned integer

Mails are autoexpunged until mail count is at or below this number of messages.

Once this threshold has been reached, mailbox_autoexpunge processing is done.

mailbox_name

Default	[None]
Value	string

Name of the mailbox being configured. The mailbox filter name refers to this setting.

mailbox_special_use

Default	[None]
Value	Boolean List
Changes	Changed: 2.4.0 Using non-standard special-use flags will result in a warning message at startup.

List of SPECIAL-USE (RFC 6154) flags to broadcast for the mailbox.

There are no validity checks, so you could specify anything you want here, but it's not a good idea to use other than the standard ones specified in the RFC.

Example

namespace inbox {
  # the namespace prefix isn't added again to the mailbox names.
  #prefix = INBOX.
  inbox = yes
  # ...

  mailbox Trash {
    auto = no
    special_use = \Trash
  }

  mailbox Drafts {
    auto = no
    special_use = \Drafts
  }

  mailbox Sent {
    auto = subscribe # autocreate and autosubscribe the Sent mailbox
    special_use = \Sent
  }

  mailbox "Sent Messages" {
    auto = no
    special_use = \Sent
  }

  mailbox Spam {
    auto = create # autocreate Spam, but don't autosubscribe
    special_use = \Junk
  }

  mailbox virtual/All { # if you have a virtual "All messages" mailbox
    auto = no
    special_use = \All
  }
}