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Create and Manage Shared Mailboxes in Cyrus-Imap

Shared mailboxe are a very convenient way to access the content of a mailbox from different accounts. The situation I'm going to describe here is the following:

  1. “” is an email address that is publicly accessible. Many emails arrive on this address and need to be answered by 2 different persons: Bob and Bill.
  2. Bob and Bill have their own email accounts and their own mailboxes. We do not want to change that. We want Bob and Bill to access “contact” from their account.
  3. Alice is the boss. She wants to be able to access the “contact” mailbox. But she does not want to mark or delete messages.

So, we are going to create “” as a shared mailbox and give accesses to Bob, Bill and Alice. Here is how.


Shared mailboxes are a bit special. Unlike regular mailboxes, they do not require a valid user on the system. Cyrus will use a internal “postuser” to determine the destination of incoming messages. When Postfix (or any SMTP server) receives an email for “”, it will forward it to “”. Cyrus will translate this destination address as “This is a message for a shared folder because it starts with postuser 'sharedboxmngr': deliver it to mailbox located into”.

<note>This is explained in the man page of imapd.conf</note>

Configure Cyrus-Imap 2.2

First, we create the postuser in /etc/imapd.conf:

# vim /etc/imapd.conf
postuser: sharedboxmngr

The altnamespace parameter also need to be changed from 'no' to 'yes' in /etc/imapd.conf.

# Alternate namespace
# If enabled, activate the alternate namespace as documented in
# /usr/share/doc/cyrus-doc-2.2/html/altnamespace.html, where an user's
# subfolders are in the same level as the INBOX
# See also userprefix and sharedprefix on imapd.conf(5)

altnamespace: yes

Then, restart cyrus-imap and create the shared mailbox in the cyradm interface.

# /etc/init.d/cyrus2.2 restart
Stopping Cyrus IMAPd: cyrmaster.
Waiting for complete shutdown...
Starting Cyrus IMAPd: cyrmaster.

# cyradm --user cyrus localhost
localhost> cm

The mailbox should appear in the main partition of Cyrus-Imap. The default on Debian is /var/spool/cyrus/mail so the mailbox is stored at /var/spool/cyrus/mail/c/shared/contact.

Access Control List

ACLs are of the following types:

Access rightDescription
l Look up the name of the mailbox (but not its contents). (visible to LIST/LSUB/UNSEEN)
r Read the contents of the mailbox. (SELECT, CHECK, FETCH, PARTIAL, SEARCH, COPY source)
s Preserve the “seen” and “recent” status of messages across IMAP sessions. (STORE \SEEN)
w Write flags other than \SEEN and \DELETED.
i Insert (move or copy) a message into the mailbox. (APPEND, COPY destination)
p Post (send mail to mailbox)
c Create a new mailbox below the top-level mailbox (ordinary users cannot create top-level mailboxes) (CREATE new sub-mailboxes, RENAME or DELETE mailbox)
d Delete a message and/or the mailbox itself. (STORE \DELETED, EXPUNGE)
a Administer the mailbox (change the mailbox's ACL) (SETACL)

To allow incoming messages to be delivered to this mailbox, we need to give the p permission to everybody:

localhost> setaclmailbox anyone p

To allow Bob and Bill to read, mark, write and delete in this mailbox, we give them the lrswipcd permissions:

localhost> setaclmailbox bob lrswipcd
localhost> setaclmailbox bill lrswipcd

To allow Alice to read the content of the mailbox, we give her the lr permissions. Since we do not give her the s permission as well, she cannot mark a message as “read” (the SEEN flag is not stored).

localhost> setaclmailbox alice lr

<note>Instead of setaclmailbox, you can use 'setacl' or 'sam'. They mean the same thing.</note>

Now, the mailbox should appear to Bob, Bill and Alice. In Thunderbird, go to the Subscribe control panel and check the shared mailbox.

Configure Postfix

This “contact” shared mailbox is not a regular user. Therefore, Postfix cannot just forward it to cyrus like any other mail. It needs to translate “” into “”. We can do that with an alias.

There are many ways to manage aliases, but the basic one is to add a new line into /etc/aliases, as follow:

# vim /etc/aliases

# postalias /etc/aliases

And that's it. Postfix should translate the alias before forwarding the email to cyrus, and cyrus will store it in the shared mailbox.

en/ressources/dossiers/cyrus/shared_mailbox.txt · Last modified: 2024/04/17 10:19 by