Install postfix-policyd-spf-perl by entering the following commands in the terminal:
sudo apt update sudo apt install postfix-policyd-spf-perl
Description:
Simple Postfix policy server for RFC 4408/7208 SPF checking
postfix-policyd-spf-perl is a basic Postfix SMTP policy server for SPF checking. It is implemented in pure Perl and uses the Mail::SPF module. The SPF project web site is http://www.openspf.net/.
Homepage: https://launchpad.net/postfix-policyd-spf-perl/
Version: 2.010-2
Section: universe/mail