PostFix - Masquerade all Outgoing mail but not Local

[Vince0000]

Hi Guys,

Just curious if anyone can assist me in setting up Postfix to masquerade the way that I need too. I have a working Sendmail Setup and everything is working good so far but I wanted to experiment and see what Postfix was all about as I heard good things about it.

I have mail sending and receiving fine except for one issue. When I send a mail from say User@this.domain.com to another local user it works good and If it is not to another local user (Outgoing Mail) I want it to masquerade as User@domain.com for outgoing mail...
I setup the masquerade Domain ltem but everything gets masqueraded as XXX@domain.com which is no good becuase if a local user mails a local user and it gets masqueraded to XXX@domain.com it now has to go back to the ISP or relay instead of staying local.

Can anyone assist me in this issue?
Thanks,
Vince

 

[Vince0000]

Here is another example in case the previous doesn't make sense...

usera@this.domain.com -----mails------------ userb@this.domain.com

keeps the usera@this.domain.com address which is fine

Usera@this.domain.com -----mails------------ JoeBlow@hotmail.com

should be masqueraded as Usera@domain.com

Thanks,
Vince