I have one local server in my office running zimbra with split dns setup. and one on public which is run by hosting provider not running zimbra.

server on local is - zimbra.mydomain.com
server on public is - mail.mydomain.com

I use fetchmail to download mail to zimbra.mydomain.com from mail.mydomain.com. User abc@mydomain.com works outside the local network so his mail client is configured to use mail.mydomain.com.

Question is, if someone from local network send an email to abc@mydomain.com it should be forwarded to mail.mydomain.com. Otherwise the mails for abc@mydomain.com need to be checked only from local network. Is there any configurations to accomplish or any other suggestions solve this issue.