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I have a barracuda server that receives mails, filter them and forward to a
linux system running postfix.

Both machine have a public IP (static).

The linux system is configured to be used as SMTP for sasl authenticated
users as well, besides to be used as SMTP for the people on $mynetworks
(permit_mynetworks in the smtpd_recipient_restrictions).

Unfortunatley, some spammers, have found it and use to spam local recipients
using the linux machine, avoiding so to be filtered through the barracuda
system.

I'm wondering if there is a way to allow OLNY local users or users belonging
to the doma