Mail Namespace

src/lib-storage/mail-namespace.h describes mail namespaces. See Namespaces for more information about what they are actually about.

Hierarchy Separators and Namespace Prefixes

A namespace and mailbox_list has 1:1 relationship. A namespace is mainly about dealing with hierarchy separators and namespace prefixes, which mailbox list doesn't know or care much about.

Mailbox lists have their native hierarchy separators. For example with FS layout the separator is '/', because child mailboxes are physically in subdirectories and '/' is the separator for directories. With Maildir++ layout the separator is hardcoded to '.' in the maildir directory name, so that's its native hierarchy separator.

Dovecot allows namespace separators to be configurable, so namespaces have two separators:

• mail_namespace_get_sep() returns the namespace's configured separator. If unset, this uses the mailbox_list's default separator.

• mailbox_list_get_hierarchy_sep() returns the mailbox_list's native separator.

All list=yes namespaces must use the same configured hierarchy separator. This is returned by mail_namespaces_get_root_sep().

Namespaces also have prefixes. The prefixes are visible for users/clients and they appear to be part of the actual mailbox name. One commonly used namespace prefix is "INBOX.", so all mailboxes (other than INBOX itself) appear to be children of the INBOX.

If all configured namespaces have a non-empty prefix, Dovecot internally creates a namespace with empty prefix. This way functions that find a namespace for a given mailbox name will always be able to return a valid namespace, so callers don't have to handle "nonexistent namespace" error.

See mailbox names for how mailbox names behave with namespace configuration.

Users and Owners

When accessing other users' shared mailboxes, there's a difference between a namespace's user and owner:

• ns->user points to the mail user actually accessing the mailbox (i.e. the IMAP connection's mail user).

• ns->owner points to the mail user who shared the mailbox.

The distinction can be important sometimes. For example if user adds or removes messages from the shared mailbox, the owner's quota must be updated instead of the user's.

Functions

Functions about finding namespaces:

• mail_namespace_find() returns namespace for given virtual name. It also has a few variations:

  • mail_namespace_find_unalias() changes the behavior for namespaces that are aliases to another namespace (namespace_alias_for). Then it returns the unaliased namespace and modifies the mailbox name.

  • mail_namespace_find_visible() skips hidden=yes namespaces.

  • mail_namespace_find_subscribable() skips subscriptions=no namespaces.

  • mail_namespace_find_unsubscribable() skips subscriptions=yes namespaces.

• mail_namespace_find_inbox() returns the namespace with inbox=yes. There is always exactly one such namespace.

• mail_namespace_find_prefix() returns the namespace that has the given prefix.

  • mail_namespace_find_prefix_nosep() does the same, but ignores the trailing separator in prefix (e.g. "foo" would find namespace with prefix=foo/).

A single namespace can in theory point to multiple storages. The ns->storage points to the default storage, while ns->all_storages is an array of all storages that the namespace can access. Currently there is no actual code that adds more than one storage to a namespace, but this might change some day so try to avoid preventing that. When creating new mailboxes, mail_namespace_get_default_storage() returns the storage that should be used. For other purposes you should find the storage via mailbox list functions.