I've been using davmail + kontact to connect to our exchange owa setup. 
Davmail enables imap/pop3, smtp, caldav and ldap support against an exchange owa setup.
The ldap lookup part has worked flawlessly in my Kubuntu 12.10 with kde 4.9, 4.9.98, 4.10 and 4.10.1 ( other minor bugs in 4.9 has been solved in later versions, such as caldav write both ways) .
After upgrading to 4.10.2 ldap lookup seem to have stopped.
I've used directions from http://forum.kde.org/viewtopic.php?f=20&t=6553&start=15 when setting this up. 
It's the part regarding ldap that doesn't work in my setup currently:
[...]
kontact => settings => Configure Kontact => Contacts => LDAP Server Settings => Add Host
Host: localhost
DN: ou=people
Authentication: Simple
Port: 1389
Bind DN: DOMAIN\username
Password: ThePassword
Click OK
Tick localhost
kontact => Mail => settings => Configure KMail => Composer => Configure completion order => and set LDAP to first
[...]

I've used a local ldap client and done lookups through davmail manually, so that part seem to work ok, I'm pretty sure this must be a bug in Kontact or any related package

Reproducible: Always

Steps to Reproduce:
1. You need access to some exchange owa account ( I've got that, and can test anything anybody suggests)
2. install davmail and point it to your exchange owa login ( see http://forum.kde.org/viewtopic.php?f=20&t=6553&start=15 for directions)
2. Setup ldap lookup in kontact
kontact => settings => Configure Kontact => Contacts => LDAP Server Settings => Add Host
Host: localhost
DN: ou=people
Authentication: Simple
Port: 1389
Bind DN: DOMAIN\username
Password: ThePassword
Click OK
Tick localhost
kontact => Mail => settings => Configure KMail => Composer => Configure completion order => and set LDAP to first
3. create a new mail, type in a couple of letters for an address you know should be in the exchange GAL .
Actual Results:  
nothing happens

Expected Results:  
kontact should suggest any email address starting with the letters you've typed