Our company is currently running a mail server with sendmail (abc@mydomain.com). I am going to replace it by zimbra. Now, I finished to set up a Zimbra server and wanna put it to the production line (replace the old sendmail server). However, I don't know how to replace it.

since the hostname of the new zimbra server is zimbra.mydomain.com. The new zimbra a/c are abc@zimbra.mydomain.com. How can I make it to be abc@mydomain.com?