postinst is in postfix-gld 1.7-3build1.
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  | #!/bin/sh
set -e
if [ "$1" = "configure" ]; then
  if ! getent passwd postfix-gld >/dev/null; then
    adduser --quiet --system --group --home / --no-create-home postfix-gld
  fi
fi
if [ -x "/etc/init.d/gld" ]; then
  update-rc.d gld defaults 19 > /dev/null
  invoke-rc.d gld start
fi
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