postinst is in amavisd-new-postfix 1:2.11.0-1ubuntu1.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92  | #! /bin/sh
# postinst script for amavisd-new-postfix
set -e
# summary of how this script can be called:
#        * <postinst> `configure' <most-recently-configured-version>
#        * <old-postinst> `abort-upgrade' <new version>
#        * <conflictor's-postinst> `abort-remove' `in-favour' <package>
#          <new-version>
#        * <deconfigured's-postinst> `abort-deconfigure' `in-favour'
#          <failed-install-package> <version> `removing'
#          <conflicting-package> <version>
# for details, see http://www.debian.org/doc/debian-policy/ or
# the debian-policy package
#
# quoting from the policy:
#     Any necessary prompting should almost always be confined to the
#     post-installation script, and should be protected with a conditional
#     so that unnecessary prompting doesn't happen if a package's
#     installation fails and the `postinst' is called with `abort-upgrade',
#     `abort-remove' or `abort-deconfigure'.
POSTFIX_BCKFILE="/var/backups/amavisd-new-postfix/main.cf-backup"
POSTFIX_MASTER_BCKFILE="/var/backups/amavisd-new-postfix/master.cf-backup"
set_postfix_option() {
       opt="$1"
       # Backup the existion value of the option
       postconf $(echo ${opt} | cut -d= -f1) >> ${POSTFIX_BCKFILE} || true
       # Set the new value of the option
               postconf -e "${opt}"
}
case "$1" in
    configure)
       if [ -f "/etc/postfix/main.cf" ]; then
		if [ -z "$2" -o ! -e "$POSTFIX_BCKFILE" ]; then
			if which postconf >/dev/null; then
				# Setup postfix
				set_postfix_option "content_filter = smtp-amavis:[localhost]:10024"
				set_postfix_option "policy-spf_time_limit = 3600s"
				SMTPD_RECIP_RESTR=`postconf smtpd_recipient_restrictions`
				set_postfix_option "$SMTPD_RECIP_RESTR, check_policy_service unix:private/policy-spf"
			fi
		cp /etc/postfix/master.cf  $POSTFIX_MASTER_BCKFILE
		postfix-add-policy policy-spf nobody /usr/bin/policyd-spf
		postfix-add-filter smtp-amavis 10025
		fi
       else
                echo ""
                echo "Postfix not configured. Run"
                echo "sudo dpkg-reconfigure postfix and choose"
                echo "the type of mail server. Then run"
                echo "sudo dpkg-reconfigure amavisd-new-postfix to"
                echo "finish amavisd-new-postfix installation."
                echo ""
       fi
       if [ -x "/etc/init.d/postfix" ]; then
               if [ -x /usr/sbin/invoke-rc.d ]; then
                       invoke-rc.d postfix restart
               else
                       /etc/init.d/postfix restart
	       fi
       fi
       if [ -x "/etc/init.d/amavis" ]; then
               if [ -x /usr/sbin/invoke-rc.d ]; then
                       invoke-rc.d amavis restart
               else
                       /etc/init.d/amavis restart
	       fi
       fi
    ;;
    abort-upgrade|abort-remove|abort-deconfigure)
    ;;
    *)
        echo "postinst called with unknown argument \`$1'" >&2
        exit 1
    ;;
esac
# dh_installdeb will replace this with shell code automatically
# generated by other debhelper scripts.
exit 0
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