postfix.init.pp: Make sure the postfix user is in the mail group.

postfix/manifests/init.pp

@@ -76,6 +76,11 @@ class postfix {
         case $::operatingsystem {
             "debian","ubuntu": {
                 package {"postgrey": ensure => installed,}
+                exec { "usermod-postfix":
+                    path    => "/bin:/usr/bin:/sbin:/usr/sbin",
+                    command => "usermod -a -G mail postfix",
+                    unless  => "id -n -G openldap | grep '\\bmail\\b'",
+                }
             }
             default: {
                 fail("Postgrey module not yet supported in ${::operatingsystem}.")