Block Spam with Mailscanner / Postfix

As a followup on my blog regarding Mailscanner as your mailrelay for your Domino environment ( link ), this article describes how to block more spam using postfix on your Linux server.

More and more, my mailbox is full of garbage from spammers. Now it’s time to block them…at least try harder to block those mail.

Add these lines into /etc/postfix/main.cf

To reject email when the HELO/EHLO hostname has neither DNS A record nor MX record, use:
smtpd_helo_required = yes
smtpd_helo_restrictions =
permit_mynetworks
permit_sasl_authenticated
reject_invalid_helo_hostname
reject_non_fqdn_helo_hostname
reject_unknown_helo_hostname

To restrict senders use:
smtpd_recipient_restrictions =
check_sender_access hash:/etc/postfix/sender_access

Edit and deploy /etc/postfix/sender_access:
Add these lines ( put your won configuration inside it )

# ADDRESS PATTERNS         # ACTION
sender@example.com         550 Blacklisted
domain.com                 REJECT
user@                      REJECT

Now build the database for postfix:
postmap /etc/postfix/sender_access
It will create the file /etc/postfix/server_access.db


Add the following lines. It will reject email if the domain name of the address supplied with the MAIL FROM command has neither MX record nor A record.
smtpd_sender_restrictions =
permit_mynetworks
permit_sasl_authenticated
reject_unknown_reverse_client_hostname
reject_unknown_sender_domain
reject_unknown_client_hostname

Don’t be an open relay:
smtpd_relay_restrictions =
permit_mynetworks permit_sasl_authenticated defer_unauth_destination

Now restart postfix: systemctl restart postfix

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