One of our partner firms is getting their own mail server, so I've got to set up their domains to be relayed to the new server until the MX changes have propagated. I don't want to delete the accounts just yet, I want to make sure everyone has copied their mail to the new server first. But all mail should be relayed, even for existing accounts?

How do I best configure this? I'm familiar with the split domain setup in the wiki. Is it enough to set zimbraMailTransport for each domain that will be moving, or should I set it for each account in those domains as well?