[CentOS] masquerade from - postfix

Hello guys,

recently my mail provider started blocking mails from non-existent domain.

We use for internal purposes domain labs.hlacik.eu which exists only in our local DNS servers. Our mailserver is sx1.labs.polarion.com . As we use virtual domains configuration & mailman i want to keep it that way == unchanged myorigin or mydomain.

What i want to setup is just masquerading for mails sent from localhost.

As example mail from root@sx1.labs.polarion.com should be masqueraded to mail from root@polarion.com and etc. This is very easy fix in sendmail, but how to do this in postfix - and not to break virtual domains configuration.

Thanks in advance!

David