blocking access to certain aliases based on domain or ip?

[Christian Nygaard]

I'm using a Postfix and a Mailscanner setup.

How do I only allow access to certain email alias addresses in
/etc/postfix/aliases based on the sender domain or ip.

In this case my own domain is example.com and it contains
an examplealias which points to certain local users. Users
from outside the network/domain may not send email
to that alias.

Only allow
  Mail to: examplealias at example.com
  From: example.com or 192.168.0.0/24
(if its a ip block or domain block doesnt matter)

Recejet all other senders trying to send email to examplealias at example.com
(It would be nice if one could return an SMTP error code if the sender is
not allowed
to send to the alias.)

How do I do that?

Thanks for your input!
Chris
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