procmail:
  debug_print = "R: procmail for $local_part@$domain"
  driver = accept
  domains = +local_domains
  check_local_user
  transport = procmail_pipe
  # emulate OR with "if exists"-expansion
  require_files = ${local_part}:\
                  ${if exists{/etc/procmailrc}\
                    {/etc/procmailrc}{${home}/.procmail.d/procmailrc}}:\
                  +/usr/bin/procmail
  no_verify
  no_expn