** Configuration **
namespace shared {
prefix = user/%u/
location = maildir:/home/%u/Maildir:INDEX=~/Maildir/shared-indexes
}So the only difference to how it's configured now is that %u is expanded to whatever user whose mailboxes we're accessing. ACL plugin then uses that user as the owner in the namespace's mailbox owner. Since the default ACL is to not give any access to non-owners, the mailboxes without dovecot-acl files will be invisible.
If ACL plugin isn't loaded, I suppose the mailboxes can be accessed if the process has filesystem permissions to access them.
** ACL vfile speedups **Currently it stat() the dovecot-acl file a bit too often. It doesn't do it more than once a second, but there's really no need to do it even that often. I guess it could be changed to be configurable with default being something like 5 minutes.
Create a new dovecot-acl-list file which lists all the mailboxes which have dovecot-acl file with "l" right (visible in mailbox list) to any non-owner. It could be in "<timestamp> <mailbox name>" format. This allows other users to quickly get a list of mailboxes that are potentially visible to them. They still need to read the dovecot-acl file from the mailbox before knowing for sure.
If the dovecot-acl-list file doesn't exist or if at any time any timestamp doesn't match dovecot-acl file's current mtime, the file is rebuilt by looking into all mailboxes' dovecot-acl files (if the reading user has write permissions to the directory, otherwise it just keeps it in memory). Whenever Dovecot modifies dovecot-acl file, it also updates the dovecot-acl-list file. This means that the file can contain stale data only if a new dovecot-acl file is created without updating dovecot-acl-list file. Even that will be fixed the next time the owner does a LIST (or select the mailbox, or anything that causes its dovecot-acl file to be stated), which causes ACL plugin to notice the desync.
There exist also global ACL files. These need to be included in the dovecot-acl-list file as well. The only issue with them is that user doesn't necessarily have a mailbox even though the global ACL file exists. So these need to be marked somehow in the dovecot-acl-list file as non-existing mailboxes. Then if user creates a mailbox with such name, the mark is removed. Deleting the mailbox puts the mark back.
After the visible mailbox list has been figured out once, only the dovecot-acl-list file needs to be stat()ed once in a while instead of all the mailboxes' dovecot-acl files.
** User list **The next problem is how to quickly get a list of users whose mailboxes are visible to ourself so they can be included in mailbox list. I couldn't figure out anything new and great for this, so the options are the same as in http://dovecot.org/list/dovecot/2006- October/017082.html
Although for dict backend I could make it a bit more secure. Currently dict has "private" and "shared read-write" options to store the data with. The shared users list could be done with "shared read- only".
** Virtual domains **ACL plugin could support virtual "[EMAIL PROTECTED]" to give access to usernames ending with @domain. Or perhaps the group could support wildcards? "[EMAIL PROTECTED]"? That way it wouldn't be required to have @ really in the username.
Anyway, I think "anyone" should then be aliased to "[EMAIL PROTECTED]". If there are multiple virtual domains and you let the users manipulate the ACLs themselves, I'd think they want anyone to mean anyone within my domain (my organization) rather than really anyone who just happens to be using the same server.
I think it would also be annoying if anyone could really force their own mailboxes to be visible to a lot of people. That could be used for spamming as well..
If administrator wants to have global mailboxes that really are visible to all domains, they could be done with public namespaces (not shared).
** Quota **This is kind of problematic. The behavior depends entirely on quota backend:
- Filesystem quota of course tracks the quota based on the file's owner
- Maildir++ quota counts the quota for the user whose maildir the shared mailbox exists in. This means it also requires filesystem level access to maildirsize file, otherwise the quota updating happens sometimes later when the quota is recalculated.
- Dict quota.. I think it'll need a new path for each shared mailbox, which is modifiable by any user. So while your own quota would exist in private/quota/storage, the shared mailboxes' quota would exist in shared/quota/storage. This means that the dict quota needs to be able to know what mailboxes the current user has shared. It also gets a bit tricky to update the quota if mailbox is unshared. The quota could be tracked individually for each mailbox also, but I'm not sure if that's such a great idea either.
Perhaps a new quota backend could be implemented to make all this easier. The mail sizes could be tracked in index file, so getting the size of a mailbox could be done simply by reading the value from the index file's header. With mailbox list indexes (in CVS HEAD) they'd all be listed in a single mailbox.list.index file, which would make summing them up really fast. This would require that users don't use private index files for shared mailboxes though. But if the users don't have shell access the shared index files are probably a good idea anyway (at least from performance point of view).
** Symlink shares **Currently the only way to implement shared mailboxes among users is for administrator to create symlinks. This will be possible in future too with a configuration like:
namespace shared {
prefix = Shared/
location = maildir:~/Maildir/shared-symlinks:INDEX=~/Maildir/
shared-indexes
}The "owner" ACL won't match anyone. So it'll work exactly as it does now.
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