postfix newbie question

[Florian Kohl <floh_(_at_)_blafasel_(_dot_)_org>]

Hi list,

my Postfix install will not forward mail to other domains, when I try to
mail from a remote ISP. It will only accept to relay mails within it´s
domain (blafasel.org).

Please reply off list since this really is a stupid question...