I have a customer who moved off the zimbra system onto their own Exchange server. I can't send them email anymore because zimbra wants to deliver to their zimbra domain accounts. I'd like to disable their domain so email I send them goes to their new email server but I'd like to preserve their accounts in case they need to get any info out that may have been missed.

Is there any way to do this? I thought about just renaming the domain but that doesn't appear to be an option.