diff --git a/target/start-mailserver.sh b/target/start-mailserver.sh
index 07aa378f..d688b51d 100644
--- a/target/start-mailserver.sh
+++ b/target/start-mailserver.sh
@@ -39,6 +39,7 @@ DEFAULT_VARS["SRS_SENDER_CLASSES"]="${SRS_SENDER_CLASSES:="envelope_sender"}"
 DEFAULT_VARS["REPORT_RECIPIENT"]="${REPORT_RECIPIENT:="0"}"
 DEFAULT_VARS["LOGROTATE_INTERVAL"]="${LOGROTATE_INTERVAL:=${REPORT_INTERVAL:-"daily"}}"
 DEFAULT_VARS["LOGWATCH_INTERVAL"]="${LOGWATCH_INTERVAL:="none"}"
+DEFAULT_VARS["EXPLICITLY_DEFINED_SPAMASSASSIN_SPAM_TO_INBOX"]="$( [ -z "${SPAMASSASSIN_SPAM_TO_INBOX}" ] && echo "0" || echo "1" )" # used for backward compatibility
 DEFAULT_VARS["SPAMASSASSIN_SPAM_TO_INBOX"]="${SPAMASSASSIN_SPAM_TO_INBOX:="0"}"
 DEFAULT_VARS["MOVE_SPAM_TO_JUNK"]="${MOVE_SPAM_TO_JUNK:="1"}"
 DEFAULT_VARS["VIRUSMAILS_DELETE_DELAY"]="${VIRUSMAILS_DELETE_DELAY:="7"}"
@@ -100,7 +101,7 @@ function register_functions() {
 
 	if [ "$SMTP_ONLY" != 1 ]; then
 		_register_setup_function "_setup_dovecot"
-                _register_setup_function "_setup_dovecot_dhparam"
+    _register_setup_function "_setup_dovecot_dhparam"
 		_register_setup_function "_setup_dovecot_quota"
 		_register_setup_function "_setup_dovecot_local_user"
 	fi
@@ -1492,9 +1493,12 @@ function _setup_security_stack() {
 				sed -i "s/\$final_spam_destiny.*=.*$/\$final_spam_destiny = D_PASS;/g" /etc/amavis/conf.d/49-docker-mailserver
 				sed -i "s/\$final_bad_header_destiny.*=.*$/\$final_bad_header_destiny = D_PASS;/g" /etc/amavis/conf.d/49-docker-mailserver
 		else
-		    notify 'warn' "Spam messages WILL NOT BE DELIVERED, you will NOT be notified of ANY message bounced.  See SPAMASSASSIN_SPAM_TO_INBOX options."
 		  	sed -i "s/\$final_spam_destiny.*=.*$/\$final_spam_destiny = D_BOUNCE;/g" /etc/amavis/conf.d/49-docker-mailserver
 				sed -i "s/\$final_bad_header_destiny.*=.*$/\$final_bad_header_destiny = D_BOUNCE;/g" /etc/amavis/conf.d/49-docker-mailserver
+
+				if [ "${DEFAULT_VARS['EXPLICITLY_DEFINED_SPAMASSASSIN_SPAM_TO_INBOX']}" = 0 ]; then
+          notify 'warn' "Spam messages WILL NOT BE DELIVERED, you will NOT be notified of ANY message bounced. Please define SPAMASSASSIN_SPAM_TO_INBOX explicitly."
+        fi
 		fi
 
 	fi
diff --git a/test/mail_spam_bounced.bats b/test/mail_spam_bounced.bats
index c194b25b..9b0880fc 100644
--- a/test/mail_spam_bounced.bats
+++ b/test/mail_spam_bounced.bats
@@ -14,18 +14,27 @@ function teardown() {
 }
 
 function setup_file() {
-    docker run -d --name mail_spam_bounced \
+    docker run -d --name mail_spam_bounced_defined \
 		-v "`pwd`/test/config":/tmp/docker-mailserver \
 		-v "`pwd`/test/test-files":/tmp/docker-mailserver-test:ro \
 		-e ENABLE_SPAMASSASSIN=1 \
 		-e SPAMASSASSIN_SPAM_TO_INBOX=0 \
 		-h mail.my-domain.com -t "${NAME}"
 
-    wait_for_finished_setup_in_container mail_spam_bounced
+    wait_for_finished_setup_in_container mail_spam_bounced_defined
+
+    docker run -d --name mail_spam_bounced_undefined \
+		-v "`pwd`/test/config":/tmp/docker-mailserver \
+		-v "`pwd`/test/test-files":/tmp/docker-mailserver-test:ro \
+		-e ENABLE_SPAMASSASSIN=1 \
+		-h mail.my-domain.com -t "${NAME}"
+
+    wait_for_finished_setup_in_container mail_spam_bounced_undefined
 }
 
 function teardown_file() {
-    docker rm -f mail_spam_bounced
+    docker rm -f mail_spam_bounced_defined
+    docker rm -f mail_spam_bounced_undefined
 }
 
 @test "first" {
@@ -33,14 +42,27 @@ function teardown_file() {
 }
 
 @test "checking amavis: spam message is bounced" {
-  run sh -c "docker logs mail_spam_bounced | grep 'Spam messages WILL NOT BE DELIVERED'"
+  # this warning should only be raised when no explicit value for SPAMASSASSIN_SPAM_TO_INBOX is defined
+  run sh -c "docker logs mail_spam_bounced_defined | grep 'Spam messages WILL NOT BE DELIVERED'"
+  assert_failure
+
+  # send a spam message
+  run docker exec mail_spam_bounced_defined /bin/sh -c "nc 0.0.0.0 25 < /tmp/docker-mailserver-test/email-templates/amavis-spam.txt"
+  assert_success
+
+  run repeat_until_success_or_timeout 20 sh -c "docker logs mail_spam_bounced_defined | grep 'Blocked SPAM {NoBounceInbound,Quarantined}'"
+  assert_success
+}
+
+@test "checking amavis: spam message is bounced, undefined SPAMASSASSIN_SPAM_TO_INBOX raise a warning" {
+  run sh -c "docker logs mail_spam_bounced_undefined | grep 'Spam messages WILL NOT BE DELIVERED'"
   assert_success
 
   # send a spam message
-  run docker exec mail_spam_bounced /bin/sh -c "nc 0.0.0.0 25 < /tmp/docker-mailserver-test/email-templates/amavis-spam.txt"
+  run docker exec mail_spam_bounced_defined /bin/sh -c "nc 0.0.0.0 25 < /tmp/docker-mailserver-test/email-templates/amavis-spam.txt"
   assert_success
 
-  run repeat_until_success_or_timeout 20 sh -c "docker logs mail_spam_bounced | grep 'Blocked SPAM {NoBounceInbound,Quarantined}'"
+  run repeat_until_success_or_timeout 20 sh -c "docker logs mail_spam_bounced_defined | grep 'Blocked SPAM {NoBounceInbound,Quarantined}'"
   assert_success
 }