Postfix adress rewrite only for outgoing mail (to smarthost eg.)

[Christian Rößler]

Hallo,

I have a problem I am having difficulties to solve.

An user has an email like user at domain.com. He has also an alias like
user at otherdomain.com. I want the (from) adress user at otherdomain.com
rewritten to user at domain.com, but only when this mail goes to the
outside, eg. to an ISPs smarthost.

Of course it is not difficult to set
smtp_generic_maps = hash:/kolab/etc/postfix/absender_rewrite
im main.cf.

I thought setting
-o smtp_generic_maps=          (empty)
in master.cf behind the entries 127.0.0.1:10025 (SMTP interface for
injecting mail back into postfix from kolabfilter) and 127.0.0.1:10026
(SMTP interface for injecting mail back into postfix from amavis) would
suffice that only mail adresses going to the outside would be rewritten.

But that is not so.
Has anyone a hint how I may reach the goal described above?

Best regards,
Christian