On 9/14/2020 1:19 PM, Matej Tyc wrote:
Hello,
I am relatively new to the world of MTAs and MDAs, and I try to set up
shared mailboxes.
So far I have somehow succeeded - I have defined a shared namespace and
I have managed to create per-mailbox ACL files thanks to the doveadm
command.
However, I have been following these resources and there were bits that
have puzzled me:
When learning about how ACL work in e.g.
https://doc.dovecot.org/settings/plugin/acl/ - when one wishes to use
the Global ACL file, how does one link it to a particular user's
mailboxes? Examples that are listed in the documentation are far too
generic. For example does "* user=foo lrw" imply that all mailboxes of
all accounts are shared to the user foo? The doveadm command works only
if dovecot is set up with per-mailbox ACL files, so I can't use it to
reverse-engineer the correct syntax.
The global ACLs are...global. They apply to all matching mailboxes
system-wide. So to answer your question, yes "* user=foo lrw" means all
mailboxes of all accounts are shared to the user foo. But...
An interesting aspect to ACLs are dictionaries. I understood it as some
kind of cache - if there is no dictionary or it is empty, then shared
mailboxes don't work. Conversely, dictionary itself is not enough, one
needs actual ACLs set up correctly. Is this a correct understanding?
The ACLs grant/deny access to a specific mailbox - when that mailbox is
known to the client. But ACLs are never scanned or iterated over to
generate a list of available mailboxes - that's where the dictionary
comes in. The dictionary is a list of shared mailboxes - but that's all
it is. So when a client queries the server for a list of available
mailboxes the dictionary is consulted. The ACLs are then applied for
each transaction whenever a client tries to read/write/access/whatever a
specific mailbox. So theoretically, if you can manually specify the
shared mailbox correctly, no dictionary is required for access.
Next what https://wiki.dovecot.org/SharedMailboxes/Shared and
https://wiki.dovecot.org/Dictionary describe is a possibility to
reference LDAP data to define an ACL dictionary. Do I understand it
correctly that if a LDAP database is the single source of truth, then I
don't have to worry about updating dictionaries as long as LDAP itself
is up-to-date, but I have to keep ACLs and LDAP in sync manually (or
using an application)?
Again, a dictionary is a list of shared mailboxes - not ACL's. You can
use any dictionary source Dovecot can read from - but if the dictionary
also supports writing then any manipulation of ACLs will automatically
update the dictionary.
What the above implies, and I will now state explicitly, is that while
global ACLs provide *access* they do not *publish* that access. A
dictionary must be manually updated to list those mailboxes.
--
Daniel