steve288
Your knowledge seems poor, so therefore you are dangerous (technically speaking). You need to get up to speed and stop trying to do things that you do not understand. Or to say it the other way around, you need to understand and learn how to use the tools, before deciding to do things with the tools, that way you will know what you can and cannot do.
In the dungog mailsorting wiki it clearly says:
"The rules that you define are executed as email arrives in your mailbox on the server, and are independent of your email client. If you sort to folders you will need to use a IMAP mail client to read them."
Note is says "...arives in your mailbox on the server....", referring to the sme mail server.
If you delegate mail (to a server running exchange), then the latter stages of mail processing for all users is handled by exchange. You will need to use exchange to apply any delivery rules, or otherwise setup delivery rules in individual mail clients ie Outlook etc (or Thunderbird).
Thunderbird is the accepted "standard" for email clients.
IMAP is just a mail storage/delivery method. With IMAP, all mail delivered to end user accounts stays on the sme (mail) server in the users IMAP Inbox or other folders.
With POP, users download the messages from the server to their local email program.
Horde (webmail) already works with IMAP, as it reads the IMAP folders on the sme server. Horde is a web based email application running on the server, already configured to read the IMAP mail for users. There is nothing to do to make it work, so I don't understand what problems you could be having. Of course it can only read mail delivered to end user accounts (IMAP folders) on the sme server, and therefore will not be able to read mail delegated to other servers.
I think the general suggestion being made was to stop delegation to exchange, and then allow your sme server (using mailsorting or procmail) to process all mail to end user accounts, and if required to sort to other IMAP folders you create.
Then on your Windows clients, you install Thunderbird email program, and configure it to read the IMAP mail folders on the sme server.
Of course any email program can read the IMAP mail folders on the sme server, even Outlook or Outlook Express etc.
The above does away with using exchange though, which may not be what your organisation wants.