split domain questions sendmail to zimbra

[eaperezh]

Hi, Im almost ready with my split domain configuration. Just need some advice on the sendmail part.
So far I have:
zimbra.mydomain.com sending/receiving to/from the internet
if account is not local on zimbra, then forward to sendmail.mydomain.com.
So far so good.
But one thing is missing. My old users on the sendmail server(pop3/imap/webmail).
How do they send email to the users in the zimbra system? I read the split domain wiki, but i does not tell me how to do that.

Where do I tell sendmail that if mail for bar@mydomain.com cannot be delivered locally (because the user is now on zimbra) then please forward to the zimbra server?

thanks,