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Cyrus IMAP autocreate Inbox patch

NOTE : This patch has been created at the University of Athens. For more info, as well 
as more patches on Cyrus IMAPD server, please visit 

The design of Cyrus IMAP server does not predict the automatic creation of users'
INBOX folders. The creation of a user's INBOX is considered to be an external task,
that has to be completed as part of the user email account creation procedure. 
Hence, to create a new email account the site administrator has to:

  a) Include the new account in the user database for the authentication procedure
     (e.g. sasldb, shadow, mysql, ldap).
  b) Create the corresponding INBOX folder. 

Alternatively, the user, if succesfully authenticated, may create his own INBOX folder,
as long as the configuration of the site allows it (see "autocreatequota" in imapd.conf).
Unlike what not careful readers may think, enabling the "autocreatequota" option, doesn't 
lead to the automatic INBOX folder creation by Cyrus IMAP server.
In fact, "autocreate" means that the IMAP clients are allowed to automatically create 
the user INBOX. 

This patch adds the functionality of automatic creation of the users' INBOX folders into
the Cyrus IMAP server. It is implemented as two features, namely the  "create on login"
and "create on post".

Create on login
This feauture provides automatic creation of a user's INBOX folder when all of the 
following requirements are met:

i)  The user has succesfully passed the authentication procedure.

ii) The user's authorisation ID (typically the same as the user's
authentication ID)  doesn't belong to the imap_admins or admins
accounts (see imapd.conf).

iii) The "autocreatequota" option in the imap configuration file 
has been set to a non zero value. 

iv) The corresponding to the user's authorisation ID INBOX folder
does not exist.

The user's first login is the most typical case when all four requirements are met. 
Note that if the authenticated ID is allowed to proxy to another account for which 
all of the above requirements are met, the corresponding INBOX folder for that account 
will be created.

Create on post
This feauture provides automatic creation of a user's INBOX folder when all of the 
following requirements are met. 

i) An email message addressed to the user has been received.  

ii) The recipient is not any of the imap_admins or admins accounts. 
Note that passing emails to admins or imap_admins accounts from 
the MTA to LMTP should be avoided in any case.

iii) The recipient's INBOX does not exist.

iv) The "autocreatequota" option in the imap configuration file 
has been set to a non zero value. 

v) The "createonpost" option in the imap configuration file 
has been switched on. 

Besides the automatic creation of INBOX folder, additional functionalities are

  (A) Automatic creation of INBOX subfolders controlled by "autocreateinboxfolders"
configuration option. eg 

autocreateinboxfolders: sent|drafts|spam|templates

  (B) Automatic subscription of INBOX subfolders controlled by "autosubscribeinboxfolders"
configuration option. eg

autosubscribeinboxfolders: sent|spam

Obviously, only subscription to subfolders included in the "autocreateinboxfolder"
list is meaningful. 

  (C) Automatic subscription to shared folders (bulletin boards). The user gets
automatically subscribed to the shared folders declared in the "autosubscribesharedfolders"
configuration option in imapd.conf.
eg autosubscribesharedfolders: public_folder | public_folder.subfolder

In order the above action to succeed, the shared folder has to pre-exist the INBOX creation
and the user must have the appropriate permissions in order to be able to subscribe to the
shared folder.

* A new config option has been added. 'autosubscribe_all_sharedfolders' is a yes/no
option. When set to yes, the user is automatically subscribed to all shared folders one 
has permission to subscribe to. Please, note that when this option is set to yes, then
'autosubscribesharedfolders' option is overriden.

  (D) Automatic creation of a predefined default sieve script.

This is very useful when a default sieve script is used for every user. Usually, a
default anti-spam script may me be written in a file and copied to each user
sieve scripts upon the INBOX creation. The imapd.conf options that have been added
are 'autocreate_sieve_script', 'autocreate_sieve_compiledscript' and 

autocreate_sieve_script configuration option refers to the full path of the file 
that contains the sieve script. The default value is null and if no file is defined,
then no default script is created upon INBOX creation. (The feature is disabled)
eg autocreate_sieve_script: /etc/default_sieve_script

autocreate_sieve_compiledscript configuration option refers to the full path of the
file that contains the bytecode compiled sieve script. If this filename is defined
in imapd.conf and the file exists, then it is automatically copied in the user's sieve
directory. If it is not defined, then a bytecode sieve script gets on the fly compiled
by the daemon. 
eg autocreate_sieve_compiledscript: /etc/default_sieve_script.bc

generate_compiled_sieve_script is a boolean option that triggers the compilation of the 
source sieve script to bytecode sieve script. The file that the bytecode script will
be saved is pointed by autocreate_sieve_compiledscript.

Ways of compiling a sieve script : 
1. Compile a sieve script using the standard sievec utility, distributed by CMU
2. Compile a sieve script using the compile_sieve utility, released by UoA. This 
   tool is almost identical to the sievec utility, with the difference that it 
   reads the input and output file from autocreate_sieve_script and 
   autocreate_sieve_compiledscript options in imapd.conf
3. Let cyrus create a compiled sieve script using a source script. Cyrus can be
   instructed to save the compiled script any time a compiled script does not exist.

1. In order this functionality to work, the following requirements must have been met:
   - 'sieveusehomedir' option must be 'no' in the configuration (default).
   - 'sievedir' option must have a valid value.
2. Currently, this patch checks the validity of the source script while generating a 
   bytecode compiled script, but not the validity of the bytecode sieve script file.
   The administrator should make sure that the provided files contain a valid sieve
   script as well as the compiled script is updated every time the source script changes.

  (E) The administrator may control for which users and/or groups may the INBOXes 
automatically be created. The autocreate_users option restricts the groups
for which the patch will create the mailboxes. 

The default value of autocreate_users is anyone. So, if not set at all, the patch will 
work for all users. However, one may set:

autocreate_users: user1 user2 group:group1 group:group2

In that case, the INBOX will be created only for user1, user2 and the users that belong 
to group1 and group2. 

More refined control per service is provided by the options imap_autocreate_users,
pop3_autocreate_users and lmtp_autocreate_users. These options override the 
autocreate_users option and offer per service control.

One may want to restrict the create on post functionality only for a specific group
of users. To achieve this, the following lines must be added in the imapd.conf file:

createonpost: yes
lmtp_autocreate_users: group:groupname

Issues to be considered 

I) In order to use the create on post feauture one should be absolutely sure that: 
a) The MTA checks the validity of the email recipient before sending the email to
LMTP. This is an RFC821 requirement. This usually expands to "the mta should be 
able to use the account database as user mailbox database". 
b) Only authorised accounts/services can talk to LMTP.

II) Especially in the case of imap logins, the current patch implementation checks
for the INBOX folder existence upon login, causing an extra mailbox lookup in most 
of the cases. 
A better approach would be to chase the "IMAP_MAILBOX_NONEXISTENT" error code and
check if the error is associated with an INBOX folder. However, this would mess up
Cyrus code. The way it was implemented may not have been the most performance
optimised, but it produces a much cleaner and simple patch.

Virtual Domains Support

Virtual domains are supported by all versions of the patch for cyrus-imapd-2.2.1-BETA and 
later. However, it is not possible to declare different INBOX subfolders to be created or 
shared folders to be subscribed to for every domain.

Things to be done

1. Support MUPDATE

It is within the developers' intentions to support the mupdate protocol, but serious 
design issues on future cyrus releases have to resolved first.

2. Select different attributes (quota, partition, sieve filter, etc) depending on the group
a user belongs to. 

For more information and updates please visit