postfix server configuration

[Shrewd]

I have a server called host1.mydomain.com that is hosting a couple of websites. However, mydomain.com has its own mail server at mail.mydomain.com that is located at the other side of the country. If anyone from the other domains hosted at host1.mydomain.com try to send mail to admin@mydomain.com they get an immediate response that that recipient does not exist. The mail should be sent out to mail.mydomain.com and postfix should not reply thinking that it is hosting mail for mydomain.com

Simply, I want postfix to send and receive mail for every domain i am hosting except for the host1.mydomain.com which happens to be the name of this server! I want the rest of the sites to be able to send mail to admin@mydomain.com which is in a different network

Any ideas?

[Shrewd]

Thanks for the help! found the answer by changing mydestination = localhost.$mydomain instead of $mydomain.

Cheers