Masq Domainname when sending mail in the Internet ?

[Rene Marticke]

Hi,

I've a strange problem here.
I use the domain company.loc on my kolab system.

When i invite a member via Outlook i send the mail to meber at company.loc. 
<-- This works.
But the member replay this mail it comes from member at company.com so my 
calender doesn't know that this mailadresses are the same.

So i try to use the internal adress in the clientsettings. <-- Great now 
it works
.
.
But if i send a mail to the internet it also comes from 
member at domain.loc now :-(

So i played with masqurading domains in postfix. But either all mails 
are send with the masqed adresse or with the internal.

Is there a way to masq outgoing mails only ?

Best Regards
Rene