Enhanced e-mail SPAM protection in ISPConfig 3

The command below enables a stricter SPAM handling for postfix on ISPConfig 3 servers.

In Detail:

  • Reject sender hostnames with invalid syntax
  • Reject sender hostnames that are no fully qualified domains (e.g. reject "server1" but allow server1.domain.tld)
  • Reject sender domains that have no DNS records
  • Check sender IP addresses against realtime blacklists.

First make a backup of the postfix main.cf file in case that you want to reverse the changes later:

cp -pf /etc/postfix/main.cf /etc/postfix/main.cf.bak

Then execute this command to enable the additional spam protection functions (the command is one line!).

postconf -e 'smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_invalid_hostname, reject_non_fqdn_hostname, reject_unknown_recipient_domain, reject_non_fqdn_recipient, reject_unauth_destination, reject_non_fqdn_sender, reject_unknown_sender_domain, reject_unknown_recipient_domain, reject_rbl_client cbl.abuseat.org,reject_rbl_client dul.dnsbl.sorbs.net,reject_rbl_client ix.dnsbl.manitu.net, check_recipient_access mysql:/etc/postfix/mysql-virtual_recipient.cf, reject_unauth_destination'

Then restart postfix:

/etc/init.d/postfix restart

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