2.4.17 --> 2.5.3 Some mail folders no longer accessible

[Sunny]

On 22/09/15 11:01, Patrick Goetz wrote:
> Upgrading from 2.4.17 to 2.5.3 resulted in one very strange problem.
> Some of the users have a large number of nested mail folders.  After the
> upgrade, exactly one user found that some of his folders (say 3 out of
> 30) are now inaccessible.  In Thunderbird they show up, but are greyed
> out.  If you try to subscribe to the folder, the subscribe checkbox is
> missing.  In roundcube they aren't visible at all.
>
> This is pretty clearly a permissions problem of some kind.  The question
> is how could this happen and what's the least painless way of going
> about resetting the permissions so that he has access to these folders
> again?
>
> We're not doing anything fancy; for example, there are no shared
> folders; independent email addresses are configured for shared mail
> content and configured in the MUA.  The problem folders are in an
> unshared account.
>
> Also, the manifestation of the permissions problem isn't consistent
> across the affected folders.  As reported by the user:
>
> Archives Staff:  grayed out, cannot see email
> Archives Staff Retreat:  not grayed out, cannot see email, when you
> click on it, it says the action cannot be completed because the account
> does not exist
> General Convention Office:  not grayed out, can see email, when you
> click on it, it says the action cannot be completed because the account
> does not exist.
>
> Thanks.
> ----
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I see a similar issue with a shared mailbox in v2.3.7 some users and 
some of their subscriptions are greyed out. Rebuilding the index or 
re-adding the imap account works for a short while before it becomes 
corrupted again a week or two later. The mailbox has 1500 directories, 
162054 files and around 40GB in size - but users don't tend to subscribe 
to all folders and only downloads the headers.

Is there an optimum number of files/directories/size for a shared 
mailbox in cyrus?

Regards