How to disable IPv6 support in Postfix [Kaspersky Secure Mail Gateway]

[Antipova Anna]

Advice and Solutions (Forum Knowledgebase) Disclaimer. Read before using materials.

Problem

Currently KSMG has IPv6 support enabled in Postfix:

inet_protocols = all

However, Postfix 2.6 has a known limitation:

http://www.postfix.org/IPV6_README.html

"Postfix SMTP clients before version 2.8 try to connect over IPv6 before trying IPv4. With more recent Postfix versions, the order of IPv6 versus IPv4 outgoing connection attempts is configurable with the smtp_address_preference parameter. "

http://www.postfix.org/postconf.5.html#inet_protocols
"Postfix versions before 2.8 attempt to connect via IPv6 before attempting to use IPv4. "

Solution

Disable IPv6 to evade limitation by configuring:

KSMG1.1

inet_protocols = ipv4 in both /opt/kaspersky/klms-appliance-addon/share/templates/main.cf.template and /etc/postfix/main.cf and restarting Postfix afterwards: systemctl restart postfix

KSMG2.0

inet_protocols = ipv4 in   /opt/kaspersky/ksmg-appliance-addon/share/templates/main.cf.template Then change any setting in Web-UI Settings - Build-In MTA - Basic settings. You can change value of Message size limit (bytes) by 1