In a Mailman + ISPConfig type of setup, you may get the following error while sending an e-mail to the mailing list:

Error:

550 5.1.1 <leden@zweefvliegen-hasselt.be>: Recipient address rejected: User unknown in virtual mailbox table

When looking at the virtual aliases (in /var/lib/mailman/data/), the lists are empty.

You can resolve this by regenerating the aliases:

sudo /var/lib/mailman/bin/genaliases
sudo postmap /var/lib/mailman/data/transport-mailman
sudo postmap /var/lib/mailman/data/virtual-mailman

Afterwards, restart Postfix:

sudo service postfix restart

If you wish to restrict SMTP access via IP addresses or a network range, one way to do it would be via Postfix configuration. You can set up restrictions using a Postfix hash-table or via a cidr file. You can choose one or both methods to perform the restrictions. The end-result will be the same.

Create a text file with the addresses you would like to reject. You can choose whatever file name you wish. E.g.: /etc/postfix/smtp_client_access

Its content should be something like:

192.168.0.1 REJECT Stop mailing us192.168.0.2 REJECT Stop mailing us192.168.1 REJECT Stop mailing us

Next, postmap it by running:

postmap /etc/postfix/smtp_client_access

Then add/edit this in your main.cf:

smtpd  ...