Folders
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### Folders

Access to the mail account becomes available after a succesful "`\SMAP1 LOGIN`" or "`\SMAP1 AUTHENTICATE`" command. A mail account contains a list of folders. A folder contains a list of individual messages. A folder may also contain other folders (so-called "subfolders") instead. A folder that contains subfolders is called a "folder directory". Subfolders may also contain other subfolders, and so on.

Some SMAP servers are capable of creating hybrid folders that contain both messages and other subfolders, but SMAP clients should not depend on the server's ability to create such folders.

SMAP folders are referenced by listing the folder's name, the name of its parent folder (if any), then the name of the parent folder's parent folder, and so on. The name of the top level folder is listed first, and the name of the folder itself is listed last, and each folder's name is specified as a separate, whitespace-delimited word. Some `SMAP1` commands mark the end of the sequence of words that identifies a folder by an extra, empty word (folder names cannot be empty themselves). For example, the command to create a folder called "December" as a subfolder of another folder called "2002", which itself is a subfolder of a folder called "Important Mail" is:

CREATE "Important Mail" 2002 December

Folder names are written using the UTF-8 character set; they may contain any UTF-8 character except for U+0000 through U+001F.

SMAP servers may allow clients to create top-level folder or folder directories. SMAP servers may also prohibit clients from creating top-level folder or folder directories; instead, they provide a predefined list of top-level folder directories, such as "Private Folders" and "Public Folders", and SMAP clients are directed to to create subfolders under either top level folder directory. Servers that have this restriction should reject attempts to create top-level folders with an informative error message.

#### Creating folders and folder directories

C: CREATE "Private Folders" Todo-List
S: +OK Folder created
C: MKDIR Customers
S: -ERR Folders may not be created here. Please create a folder in
"Private Folders" or "Public Folders".

The `CREATE` command creates a new folder. The `MKDIR` command creates a new folder directory (a folder that contains other folders). The remaining words specify the name of the new folder or folder directory.

### Note

An SMAP client should not create a new folder directory until it is ready to create its first subfolder. The `MKDIR` command should be immediately followed by a `CREATE` command that creates the first subfolder in the new folder directory. Empty folder directories serve no particular purpose; SMAP servers are permitted (but not required) to omit empty folder directories when responding to a `LIST` command. An SMAP client that wishes to create a new folder directory now, and a subfolder some time later should be implicitly aware of the fact that it created a new folder directory even if a subsequent `LIST` command does not reveal its presence.

Some SMAP servers can implement hybrid folders that contain both folders and subfolders. Clients must explicitly use both `CREATE` and `MKDIR` commands, which may be used in either order. It is possible that hybrid-capable servers do not differentiate between the `MKDIR` and `CREATE` commands. Either one creates a folder that's ready to hold messages or subfolders. These servers must ignore a duplicate request to create an existing folder or folder directory (normally a server SHOULD reject such a request). This is because SMAP clients will send both command because they cannot rely on this behavior.

##### Executive Summary

- Use `CREATE` to create a folder, `MKDIR` to create a folder directory.

- Clients should create new folder directories just prior creating their first subfolder. Clients should not create new folder directories until they are ready to create the first subfolder.

- SMAP servers may ignore `MKDIR`, and treat it as a no-op, and automatically create logical folder directories on as-needed basis.

#### Deleting folders and folder directories

C: DELETE "Private Folders" Todo-List
S: +OK Folder deleted
C: RMDIR Customers
S: +OK Folder directory deleted

The `DELETE` and `RMDIR` commands are the opposite of `CREATE` and `MKDIR` commands. They delete the indicated folder or folder directory. Some SMAP servers may automatically remove a folder directory after its last subfolder is deleted. Normally a server should reject a request to remove a non-existent folder or folder directory. Servers that automatically remove empty directories should not reject requests to remove a non-existent directory, they should ignore and accept the request, but do nothing. The request to remove a non-existent directory is probably initiated by a client that just removed the last subfolder; the client cannot assume that the server will delete the empty directory, so it explicitly asks the server to do that.

#### Renaming folders and folder directories

C: RENAME "Dr. Jekyll" "" "Mr. Hyde"
S: +OK Folder renamed.
C: RENAME "Saved Mail" "Tomorrow's To-Do List" "" "Saved Mail" "To-Do Today"
S: +OK Folder renamed.

The `RENAME` command changes the name of an existing folder or folder directory. The command is followed by a whitespace-delimited word list that specifies an existing folder; then an empty word; then another whitespace-delimited word list which specifies a new name for the folder or folder directory. Both the old name, and the new name, must be complete folder name paths.

The first example above renames a folder named "Dr. Jekyll" to "Mr. Hyde". The second example renames a subfolder of "Saved Mail" named "Tomorrow's To-Do List" as "To-Do Today". Most SMAP servers can move a folder/subfolder to a different parent folder. This is done by specifying a different path for the new name.

Both folder and folder directories may be renamed. A renamed folder directory's subfolders "follow along" with their parent folder directory.

#### Listing folders

C: LIST
S: * LIST INBOX "New Mail" FOLDER
S: * LIST Drafts Drafts FOLDER
S: * LIST "Saved Mail" "Saved Mail" DIRECTORY
S: +OK Here are your folders
C: LIST "Saved Mail"
S: * LIST 2001 2001 DIRECTORY
S: * LIST 2002 2002 DIRECTORY
S: +OK Here are your folders
C: LIST "Saved Mail" 2002
S: * LIST February February FOLDER
S: * LIST January January FOLDER
S: +OK Here are your folders

The `LIST` command, without any arguments, returns a list of top level folders. A list of subfolders of an existing folder directories is returned by appending the folder name path to the LIST command.

The server responds with zero or more “* LIST” single line replies, one reply for each folder or folder directory. The next word after “* LIST” is the name of the folder or folder directory. The following word (called "description") is usually the same as the name of the folder. Certain reserved folders may have a different description (see below). The remaining words contain keywords that describe the folder's attributes. The following attributes are defined at this time:

`FOLDER`

  This is a regular folder that contains messages.

`READONLY`

  This is a read-only folder.

`DIRECTORY`

  This is a folder directory that contains other folders.

Every “* LIST” reply includes either `FOLDER` or `DIRECTORY`. Both attributes indicate a hybrid folder - a folder that contains both messages and subfolders.

##### Reserved folders and descriptions

Some SMAP servers may not allow clients to create new top-level folders. Instead, they provide a fixed set of top-level folders and folder directories, such as "INBOX", "private", and "public". Clients can only create new subfolders of the reserved folder directories. Other servers may do both: provide a fixed set of reserved, top-level folders, and allow clients to create new top-level folders.

A reserved folder is generally a symbolic representation for a special folder, or a folder directory, with a pre-defined purpose. The most common example would be the mail folder where new mail arrives; it is typically called “INBOX”. Reserved folders usually have brief, curt names, such as “INBOX”, “public”, or “private”. An SMAP server can offer a more meaningful description using the description word in the “* LIST” reply; for example: “New Mail”, “Public Folders”, or “My Folders”. If the client selects a different natural language, at login time, the server can provide a description in the selected language, but still use the same actual folder name.

SMAP clients should always use the official folder name, when referencing the folder in any SMAP command, and display the folder's description to the user (recall that for regular folders they are one and the same).

#### Getting folder status

C: STATUS FULL "Saved Mail"
S: * STATUS EXISTS=17 UNSEEN=5
S: +OK Status retrieved

The `STATUS` command returns the status of a folder. The next word after “`STATUS`” is a comma-delimited list of the following keywords. The remaining whitespace-delimited words specify a folder whose requested status should be returned.

The first word following “`STATUS`” contains a comma-delimited keyword list. The following keywords are defined at this time. Additional keywords may be added in the future. SMAP server should ignore keywords they do not recognize.

FULL

  Request the number of messages in the folder (sent as the “`EXISTS`” response), and the number of messages that do not have the `SEEN` flag set (the “`UNSEEN`” response).

CHEAP

  Same as `FULL` but return the message counts only if the server is capable of calculating the message counts cheaply and without delay. This keyword is mutually-exclusive with `FULL`. If the message counts cannot be calculated cheaply, the “`* STATUS`” response is not sent, but the server still responds with an “`+OK`”.

The server's “`* STATUS`” reply gives the requested message counts.

#### Access Control Lists

Access Control Lists (or “ACL”s) may be optionally implemented by an SMAP server. ACLs are usually implemented by servers that support shared folder access, where accounts may mutually share access to their folders, and ACLs specify which accounts may access which folders. ACLs define certain level of granularity; for example an ACL may specify that a given account may read messages in the folder, but not delete them, or add messages to the folder.

An SMAP server which implements ACLs will include “`ACL2=``method`” in its capability list. “Method” is the server's method for computing ACLs (see below).

##### Identifiers and rights

Each folder maintains a separate access control list, which applies to that folder only. An access control list consists of zero or more records. Each record contains two data items: an identifier, and rights. “Rights” is a list of zero more characters, that enumerate which kinds of access rights are given to the entity specified by the “identifier”. An identifier may take the following values:

`anyone`

  The access rights apply to all server accounts.

`anonymous`

  This is an alias for “anonymous”.

`user=``id`

  The access rights apply to account named “id”. The account name is specified using the `UTF-8` character set.

`group=``id`

  The access rights apply to a group of accounts named “id”. The group name is specified using the `UTF-8` character set. Account groups are site-specific lists, maintained in a site-defined manner. Each SMAP server implementation needs to specify separately the nature and the names of the available account groups (if they exist at all).

Access rights are specified using a list of zero or more characters, as follows:

`a`

  Administer this folder. Maintain this folder's ACLs.

`c`

  Create subfolders.

`e`

  Remove messages from this folder (the `EXPUNGE` and the `MOVE` commands).

`i`

  Insert messages into this folder (`COPY` or `MOVE` messages to this folder, and the `ADD` command).

`l`

  List this folder. This folder is visible, and is shown by the `LIST` command.

`r`

  Read, or open this folder (the `OPEN` or the `SOPEN` command).

`s`

  Add or remove the `SEEN` flag on messages.

`t`

  Add or remove the `DELETED` flag on messages.

`w`

  Add or remove any message flag, except for `SEEN` and `DELETED`; add and remove keywords.

`x`

  Delete this folder.

##### Negative rights

An access control list entry may have an identifier that begins with a dash. This access control list entry specifies a “negative right”, which revokes, rather than adds, the corresponding rights from the identifier. For example, consider the the following access control list:

    anyone      alr
    user=fred   -r

This ACL gives access, list, and read privileges to everyone, and revokes read privileges from the `fred` user. Presumably, everyone except fred can administer, list, and read the folder; while fred can only administer and read it.

##### Computing access rights

As hinted in the previous example, there may be more than one access control list entry that's applicable to a given user. The SMAP server needs to compute the actual access rights for a folder based on all applicable access control list entries. There are several approaches to do that. The SMAP server declares its chosen method of access rights computation using the “ACL2” capability. At this time, two access computation methods are defined:

ACL2=UNION

  Access rights from all applicable ACL entries are combined together, then, all negative rights from all applicable ACL entries are removed, giving the final result. This is the computation method used in the previous example.

ACL2=MOST-SPECIFIC

  Only access rights from the “most specific” ACL entries are factored in. That is, ACL entries referring specifically to the user (the “user=” ACL entries, and/or “owner” entries) are used, if present. Otherwise, any applicable “group=” entries are used, if present. Otherwise, “anyone” and “anonymous” entries are used by default.

  Multiple applicable most-specific entries are combined in the same way as the “union” method.

  Here's the equivalent “most-specific” version of the earlier example:

      anyone      alr
      user=fred   al

##### Obtaining access rights

C: ACL INBOX
S: * ACL "aceilrstwx"
S: +OK ACL retrieved

The `ACL` command computes the requesting client's access rights on the indicated folder. The whitespace-delimited words after “`ACL`” specify the folder whose access rights are computed and returned.

The server responds with a “* ACL” message, which contains a single word that lists the access rights on the given folder.

##### Retrieving access control lists

C: GETACL INBOX
S: * GETACL "owner" "aceilrstwx" "user=fred" "ace"
S: +OK ACLs retrieved

The `GETACL` command returns the access control list for the indicated folder. The whitespace-delimited words after “`GETACL`” specify the folder whose access control list is requested.

The server responds with a “* GETACL” message. The remaining whitespace-delimited words after “`* GETACL`” consist of a zero or more `identifier`/`rights` pairs. In each pair, `identifier` names the identity to which `rights` apply.

The server may respond with two or more “* GETACL” messages when the access control list is very large.

##### Modifying access rights

C: SETACL INBOX "" user=fred ace
S: * GETACL "owner" "aceilrstwx" "user=fred" "ace"
S: +OK Updated ACLs
C: SETACL INBOX "" user=fred +rwx
S: * GETACL "owner" "aceilrstwx" "user=fred" "acerwx"
S: +OK Updated ACLs

The `SETACL` command modifies rights for a single access control list identifier. The whitespace-delimited words after “`SETACL`” specify the folder whose access control list will be modified. The folder's name is followed by a single empty word, the identifier, then the requested access rights.

The existing access rights assigned to the identifier are replaced by the new rights specified in the command. If the identifier does not exist in the access control list, it is added with the specified rights.

If the access rights are prefixed by “+”, the specified rights are added to the existing rights, for this identifier. If the access rights are prefixed by “-”, the specified rights are removed from the existing rights, for this identifier. It is not an error to add an access right that already exists, or remove an access right that did not exist; in both cases the request is ignored (for that specific access right).

`identifier` may specify a negative right. When the server uses “ACL2=UNION” computation method, setting an empty access right list for an identifier will remove the identifier from the access control list.

The server responds with zero or more “`* GETACL`” messages, that return the updated access control list for this folder.

##### Deleting access rights

C: DELETEACL INBOX "" user=fred
S: * GETACL "owner" "aceilrstwx"
S: +OK Updated ACLs

The `DELETEACL` command removes an identifier from the access control list. The identifier may be a negative right. The whitespace-delimited words after “`DELETEACL`” specify the folder whose access control list will be modified. The folder's name is followed by a single empty word, than the identifier to be removed. It is not an error to name an identifier that does not exist, the request is effectively ignored (but the server still responds with “`* GETACL`” messages).

The server responds with zero or more “`* GETACL`” messages, that return the updated access control list for this folder.

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