Postfix issue

[joximu]

First: not an ispcp topic
Next: an external MTA which deliveres mails to your box does not need to be from a known IP (no mynetworks). You only need mynetworks for sending clients who cannot use smtp auth - normally this is a webserver for example - but need to use yout postfix as outgoing mailserver.
Next: use a more general server forum or better: try to understand what's going on.