apt-get install postfix-policyd-spf-python

/etc/postfix/master.cf

/etc/postfix/master.cf

policyd-spf  unix  -       n       n       -       0       spawn
    user=policyd-spf argv=/usr/bin/policyd-spf

/etc/postfix/main.cf

/etc/postfix/main.cf

policyd-spf_time_limit = 3600
 
smtpd_recipient_restrictions =
  permit_sasl_authenticated,
  permit_mynetworks,
  reject_unauth_destination,
  check_policy_service unix:private/policyd-spf

postfix check
postfix reload

Vérif

# grep SPF /var/log/mail.info
Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=209.85.216.181; helo=mail-qt0-f181.google.com; envelope-from=yourmailaddress@gmail.com; receiver=info@miyw.de