I am trying to set up synchronization with google accounts and at first it seemed to be going really well. I got the IMAP sync up and running (though it gives some timeout errors along the way since it was almost 1.9GB).

I did notice though, that the from-field was still my zimbra account when sending from zimbra using this account (though the reply-to was the gmail one). Remembering an option allowing you to let people send e-mail from any email address that I saw during initial configuration I decided to give it a try.

However, it was enough to enable this feature to break the account. Now when I try to test the account I get

Code:
System Error {XDH} (Failure)
and the account is disabled. Fortunately disabling the feature makes it work again but it's still very strange to me.

Do I need this setting to send the e-mail without my zimbra-address appearing?

Any ideas on how to trouble-shoot this further? I can't see any stack-traces or anything in the log.