further attempt to prevent broken interpolation

manifests/server.pp

diff --git a/manifests/server.pp b/manifests/server.pp
index d5d422a..57ebe7a 100644
--- a/manifests/server.pp
+++ b/manifests/server.pp
@@ -13,11 +13,11 @@
   # See the main.cf comments for help on these options
   $myhostname = $facts['networking']['fqdn'],
   $mydomain = false,
-  $myorigin = '$myhostname',
+  $myorigin = '\$myhostname',
   $inet_interfaces = 'localhost',
   $inet_protocols = 'all',
   $proxy_interfaces = false,
-  $mydestination = '$myhostname, localhost.$mydomain, localhost',
+  $mydestination = '\$myhostname, localhost.$mydomain, localhost',
   $local_recipient_maps = false,
   $luser_relay = false,
   $unknown_local_recipient_reject_code = '550',
@@ -34,7 +34,7 @@
   $home_mailbox = false,
   $mail_spool_directory = false,
   $mailbox_command = false,
-  $smtpd_banner = '$myhostname ESMTP $mail_name',
+  $smtpd_banner = '\$myhostname ESMTP $mail_name',
   $setgid_group = $::postfix::params::setgid_group,
   $mailbox_size_limit = undef,
   $message_size_limit = false,