diff --git a/install_postfix_advanced.sh b/install_postfix_advanced.sh
index 6051f8b..28eb00c 100755
--- a/install_postfix_advanced.sh
+++ b/install_postfix_advanced.sh
@@ -1010,6 +1010,10 @@ echononl "   Creeate new postfix configuration file"
 cat <<EOF > /etc/postfix/main.cf
 # ============ Basic settings ============
 
+# Disable backwards compatibility
+compatibility_level = 2
+
+
 # Debian specific:  Specifying a file name will cause the first
 # line of that file to be used as the name.  The Debian default
 # is /etc/mailname.
diff --git a/install_postfix_base.sh b/install_postfix_base.sh
index 41436b8..071d106 100755
--- a/install_postfix_base.sh
+++ b/install_postfix_base.sh
@@ -488,6 +488,10 @@ echononl "   Creeate new postfix configuration file"
 cat <<EOF > /etc/postfix/main.cf
 # ============ Basic settings ============
 
+# Disable backwards compatibility
+compatibility_level = 2
+
+
 # Debian specific:  Specifying a file name will cause the first
 # line of that file to be used as the name.  The Debian default
 # is /etc/mailname.
@@ -838,6 +842,39 @@ smtpd_tls_exclude_ciphers =
 smtpd_tls_session_cache_database = btree:\${data_directory}/smtpd_scache
 smtp_tls_session_cache_database = btree:\${data_directory}/smtp_scache
 
+
+
+#======= smtpd Restrictions  ============
+
+# smtpd_relay_restrictions
+#
+# IMPORTANT: Either the smtpd_relay_restrictions or the smtpd_recipient_restrictions 
+# parameter must specify at least one of the following restrictions. Otherwise Postfix 
+# will refuse to receive mail:
+#
+#        reject, reject_unauth_destination
+#
+#        defer, defer_if_permit, defer_unauth_destination
+#
+#
+# The upstream default is:
+#
+#    smtpd_relay_restrictions = \${{\$compatibility_level} < {1} ? {} : 
+#       {permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination}}
+#
+# AGAIN, that means: if parameter compatibility_level is not set or compatibility_level is 
+# set to '0', you MUST specify this value. Otherwise Postfix will refuse to receive mail
+# and you get the following error message:
+#
+#     fatal: in parameter smtpd_relay_restrictions or smtpd_recipient_restrictions, specify 
+#     at least one working instance of: reject_unauth_destination, defer_unauth_destination, 
+#     reject, defer, defer_if_permit or check_relay_domains
+#
+#smtpd_relay_restrictions = 
+#   permit_mynetworks, 
+#   permit_sasl_authenticated, 
+#   defer_unauth_destination
+
 EOF
 echo_ok