I've tried adding Zentyal to a Windows Domain with 2008r2 as the AD.
Couldn't get it to work at all.
Zentyal itself worked, and connected to AD successfully and without an issue. The problem came in with the way Zentyal works with AD. The users must be in the domain.local/users OU. Since I already have AD setup, it is not configured as such, nor will it change to be that way. My users sit in a different OU.
While testing out Zentyal, I tried to make it work using the Users OU it wanted. That did not allow me to enable any email accounts as the schema was different.
I gave up....In my opinion. Zentyal isn't ready to be an MS Exchange Drop in replacement as they advertise. Perhaps in a fresh domain, but not as part of an existing one.
I keep checking the forums in hopes someone has resolved the problems, as I am hopeful.