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Cyrus IMAP autocreate Inbox patch
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NOTE : This patch has been created at the University of Athens. For more info, as well 
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as more patches on Cyrus IMAPD server, please visit http://email.uoa.gr/ 
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The design of Cyrus IMAP server does not predict the automatic creation of users'
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INBOX folders. The creation of a user's INBOX is considered to be an external task,
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that has to be completed as part of the user email account creation procedure. 
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Hence, to create a new email account the site administrator has to:
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  a) Include the new account in the user database for the authentication procedure
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     (e.g. sasldb, shadow, mysql, ldap).
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  b) Create the corresponding INBOX folder. 
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Alternatively, the user, if succesfully authenticated, may create his own INBOX folder,
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as long as the configuration of the site allows it (see "autocreatequota" in imapd.conf).
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Unlike what not careful readers may think, enabling the "autocreatequota" option, doesn't 
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lead to the automatic INBOX folder creation by Cyrus IMAP server.
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In fact, "autocreate" means that the IMAP clients are allowed to automatically create 
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the user INBOX. 
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This patch adds the functionality of automatic creation of the users' INBOX folders into
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the Cyrus IMAP server. It is implemented as two features, namely the  "create on login"
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and "create on post".
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Create on login
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===============
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This feauture provides automatic creation of a user's INBOX folder when all of the 
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following requirements are met:
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i)  The user has succesfully passed the authentication procedure.
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ii) The user's authorisation ID (typically the same as the user's
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authentication ID)  doesn't belong to the imap_admins or admins
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accounts (see imapd.conf).
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iii) The "autocreatequota" option in the imap configuration file 
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has been set to a non zero value. 
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iv) The corresponding to the user's authorisation ID INBOX folder
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does not exist.
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The user's first login is the most typical case when all four requirements are met. 
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Note that if the authenticated ID is allowed to proxy to another account for which 
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all of the above requirements are met, the corresponding INBOX folder for that account 
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will be created.
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Create on post
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==============
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This feauture provides automatic creation of a user's INBOX folder when all of the 
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following requirements are met. 
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i) An email message addressed to the user has been received.  
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ii) The recipient is not any of the imap_admins or admins accounts. 
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Note that passing emails to admins or imap_admins accounts from 
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the MTA to LMTP should be avoided in any case.
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iii) The recipient's INBOX does not exist.
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iv) The "autocreatequota" option in the imap configuration file 
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has been set to a non zero value. 
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v) The "createonpost" option in the imap configuration file 
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has been switched on. 
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Besides the automatic creation of INBOX folder, additional functionalities are
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provided:
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  (A) Automatic creation of INBOX subfolders controlled by "autocreateinboxfolders"
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configuration option. eg 
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autocreateinboxfolders: sent|drafts|spam|templates
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  (B) Automatic subscription of INBOX subfolders controlled by "autosubscribeinboxfolders"
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configuration option. eg
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autosubscribeinboxfolders: sent|spam
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Obviously, only subscription to subfolders included in the "autocreateinboxfolder"
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list is meaningful. 
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  (C) Automatic subscription to shared folders (bulletin boards). The user gets
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automatically subscribed to the shared folders declared in the "autosubscribesharedfolders"
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configuration option in imapd.conf.
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eg autosubscribesharedfolders: public_folder | public_folder.subfolder
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In order the above action to succeed, the shared folder has to pre-exist the INBOX creation
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and the user must have the appropriate permissions in order to be able to subscribe to the
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shared folder.
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* A new config option has been added. 'autosubscribe_all_sharedfolders' is a yes/no
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option. When set to yes, the user is automatically subscribed to all shared folders one 
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has permission to subscribe to. Please, note that when this option is set to yes, then
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'autosubscribesharedfolders' option is overriden.
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  (D) Automatic creation of a predefined default sieve script.
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This is very useful when a default sieve script is used for every user. Usually, a
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default anti-spam script may me be written in a file and copied to each user
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sieve scripts upon the INBOX creation. The imapd.conf options that have been added
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are 'autocreate_sieve_script', 'autocreate_sieve_compiledscript' and 
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'generate_compiled_sieve_script'. 
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autocreate_sieve_script configuration option refers to the full path of the file 
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that contains the sieve script. The default value is null and if no file is defined,
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then no default script is created upon INBOX creation. (The feature is disabled)
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eg autocreate_sieve_script: /etc/default_sieve_script
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autocreate_sieve_compiledscript configuration option refers to the full path of the
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file that contains the bytecode compiled sieve script. If this filename is defined
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in imapd.conf and the file exists, then it is automatically copied in the user's sieve
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directory. If it is not defined, then a bytecode sieve script gets on the fly compiled
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by the daemon. 
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eg autocreate_sieve_compiledscript: /etc/default_sieve_script.bc
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generate_compiled_sieve_script is a boolean option that triggers the compilation of the 
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source sieve script to bytecode sieve script. The file that the bytecode script will
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be saved is pointed by autocreate_sieve_compiledscript.
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Ways of compiling a sieve script : 
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1. Compile a sieve script using the standard sievec utility, distributed by CMU
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2. Compile a sieve script using the compile_sieve utility, released by UoA. This 
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   tool is almost identical to the sievec utility, with the difference that it 
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   reads the input and output file from autocreate_sieve_script and 
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   autocreate_sieve_compiledscript options in imapd.conf
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3. Let cyrus create a compiled sieve script using a source script. Cyrus can be
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   instructed to save the compiled script any time a compiled script does not exist.
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NOTES : 
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1. In order this functionality to work, the following requirements must have been met:
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   - 'sieveusehomedir' option must be 'no' in the configuration (default).
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   - 'sievedir' option must have a valid value.
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2. Currently, this patch checks the validity of the source script while generating a 
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   bytecode compiled script, but not the validity of the bytecode sieve script file.
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   The administrator should make sure that the provided files contain a valid sieve
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   script as well as the compiled script is updated every time the source script changes.
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  (E) The administrator may control for which users and/or groups may the INBOXes 
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automatically be created. The autocreate_users option restricts the groups
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for which the patch will create the mailboxes. 
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The default value of autocreate_users is anyone. So, if not set at all, the patch will 
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work for all users. However, one may set:
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autocreate_users: user1 user2 group:group1 group:group2
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In that case, the INBOX will be created only for user1, user2 and the users that belong 
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to group1 and group2. 
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More refined control per service is provided by the options imap_autocreate_users,
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pop3_autocreate_users and lmtp_autocreate_users. These options override the 
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autocreate_users option and offer per service control.
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Example: 
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One may want to restrict the create on post functionality only for a specific group
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of users. To achieve this, the following lines must be added in the imapd.conf file:
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createonpost: yes
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lmtp_autocreate_users: group:groupname
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Issues to be considered 
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=======================
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I) In order to use the create on post feauture one should be absolutely sure that: 
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a) The MTA checks the validity of the email recipient before sending the email to
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LMTP. This is an RFC821 requirement. This usually expands to "the mta should be 
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able to use the account database as user mailbox database". 
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b) Only authorised accounts/services can talk to LMTP.
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II) Especially in the case of imap logins, the current patch implementation checks
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for the INBOX folder existence upon login, causing an extra mailbox lookup in most 
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of the cases. 
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A better approach would be to chase the "IMAP_MAILBOX_NONEXISTENT" error code and
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check if the error is associated with an INBOX folder. However, this would mess up
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Cyrus code. The way it was implemented may not have been the most performance
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optimised, but it produces a much cleaner and simple patch.
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Virtual Domains Support
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=======================
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Virtual domains are supported by all versions of the patch for cyrus-imapd-2.2.1-BETA and 
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later. However, it is not possible to declare different INBOX subfolders to be created or 
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shared folders to be subscribed to for every domain.
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Things to be done
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=================
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1. Support MUPDATE
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It is within the developers' intentions to support the mupdate protocol, but serious 
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design issues on future cyrus releases have to resolved first.
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2. Select different attributes (quota, partition, sieve filter, etc) depending on the group
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a user belongs to. 
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For more information and updates please visit http://email.uoa.gr/projects/cyrus/autocreate
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