*** Bug 607612 has been marked as a duplicate of this bug. ***

Let's have the permissions part done separately, in bug #667714, and keep this bug for "subscribe to other user's folder" only.

I made this done after some time of changing other internals. The "Subscribe to other user's folder" option is slightly hidden, it's visible in the context menu (right-click) above account's name in the folder tree of the Mail view. It's available only there, because the subscription requires CamelMapiStore for certain reasons.

The option opens dialog similar to that in evolution-exchange, containing account name (the one above which was the option called - it cannot be changed), the user name to whose folder subscribe, and a combo with few predefined folder names. The username is resolved when asked to subscribe and it should be unique. There can be written pretty anything, thus even part of the email address works (an example: if there is user@exchange.com and user2@exchange.com, and user wants to subscribe to 'user' folders, then there cannot be filled only 'user', but at least 'user@'). Maybe I'll add a picker when the chosen user name will be ambiguous.

The folder name can be also a folder ID (the hexa number). I didn't find a way how to subscribe to a folder by name, but with known folder ID user can subscribe basically to anything to which he/she has rights. I hoped that I could list approved folders for the given user, but I didn't find a way how to do that, the usual method of getting list of folders doesn't work here. I realized that Outlook 2007 allows only preselected names, no custom folders with this kind of subscription, thus we are slightly better than it.

I'll add folder ID to Permissions dialog, thus users will have an option to get it in a sane way.

Mail folders are added into the structure:
  <account>
     - Foreign folders
         - Mailbox - user name
             - foldername ...
ESource folders are added as "user name - foldername". If mail folders are added in descendant order (parents first), then they can create a folder structure, otherwise they are added directly under "Mailbox - user name" node.

I do not allow deleting foreign folders on the server, they are basically unsubscribed locally, although using Unsubscribe is preferred way of getting rid of already subscribed foreign folders, because Delete tries couple more things in evolution itself first, which can lead to undesired issues, like loosing data in subfolders.

Created commit 14377ea in ema master (3.3.5+)

(In reply to comment #3)
> ...Maybe I'll add a picker when the chosen user name will be ambiguous...

It turned out that the picker is needed for permissions dialog, thus I crated it there and reused here as well. The Subscribe dialog has now also a "Choose..." button, which searches GAL users. It's in with commit 57e756f (3.3.5+).