There is nothing wrong with this exchange (other than the fact that 
Exchange doesn't list the INBOX as "subscribed", but we already work 
around that).

You will need to debug further and find where your sever is having 
issues.  Try looking at javascript log on the browser or setting 
Horde's logging to debug and then looking for errors.

The Exchange server in question is a 2003 server, I tested with Firefox.
I activated debug logging in backends.local.php. I clicked in IMP 
"Folder options" > "Show all folders" and this results in debug file 
in a complete list of folders sent by Exchange server which I could 
not reproduce here completely:
S: * OK Microsoft Exchange Server 2003 IMAP4rev1 server version 
6.5.7638.1 (mailserver.bar) ready.
C: [LOGIN Command - username: mcc1]
S: 1 OK LOGIN completed.
C: 2 LSUB "" *
S: * LSUB () "/" "Sent Items"
S: * LSUB () "/" Trash
S: * LSUB () "/" Sent
S: * LSUB () "/" Drafts
S: 2 OK LSUB completed.
C: 3 LSUB "" "Public Folders/*"
S: 3 OK LSUB completed.
C: 4 LIST "" *
S: * LIST (\HasNoChildren) "/" Aufgaben
....
S: 4 OK LIST completed.
C: 5 LIST "" "Public Folders/*"
...
S: * LIST (\HasNoChildren) "/" {30}
S: [LITERAL DATA - 30 bytes]
S:
S: * LIST (\HasNoChildren) "/" "Public Folders/Whatever"
...
S: 5 OK LIST completed.
C: 6 LIST "" INBOX
S: * LIST (\Marked \HasNoChildren) "/" INBOX
S: 6 OK LIST completed.
C: 7 LOGOUT
S: * BYE Microsoft Exchange Server 2003 IMAP4rev1 server version 
6.5.7638.1 signing off.
S: 7 OK LOGOUT completed.

Apparently the Exchange server gives the whole list of folders to IMP 
but it then fails to display. There stays a "Loading..." statement 
forever and a httpd process freaks out on server.

At a minimum, you need to at least provide error logs and IMAP logs.



To further debug this issue, we need details of the IMP -> IMAP/POP 
communication.

To enable debugging, see instructions contained in 
imp/config/backends.php (the 'debug' config parameter).

Debugging should not be enabled on a production server,   Attach/post 
only the portion of the log that directly deals with the problem 
reported (it may be simplest to clear the log file and then perform 
the event that causes the error).

I am sorry but the behavior is different. In ticket #10726 there came 
an error message, here the Apache httpd process goes to use 100% cpu 
and no result in IMP.

Duplicate of Ticket #10726.

Hello again,
in ticket #10726 you guys found a solution to use IMP with Exchange 
IMAP. Now as one gets logged in and wants to retrieve the folder list 
from Exhange server IMP hangs and leads th a httpd process running 
with nearly 100%. Only cure is restarting Apache.
Regards