diff --git a/Makefile b/Makefile
index 3355ed04..b4e3d339 100644
--- a/Makefile
+++ b/Makefile
@@ -96,7 +96,7 @@ run:
 		-e PERMIT_DOCKER=network \
 		-e DMS_DEBUG=0 \
 		-e OVERRIDE_HOSTNAME=mail.my-domain.com \
-		-h mail.my-domain.com \
+		-h unknown.domain.tld \
 		-t $(NAME)
 	sleep 15
 	docker run -d --name mail_fail2ban \
diff --git a/target/start-mailserver.sh b/target/start-mailserver.sh
index f3ad1eff..abd22b18 100644
--- a/target/start-mailserver.sh
+++ b/target/start-mailserver.sh
@@ -23,7 +23,6 @@ DEFAULT_VARS["ENABLE_SASLAUTHD"]="${ENABLE_SASLAUTHD:="0"}"
 DEFAULT_VARS["SMTP_ONLY"]="${SMTP_ONLY:="0"}"
 DEFAULT_VARS["DMS_DEBUG"]="${DMS_DEBUG:="0"}"
 DEFAULT_VARS["OVERRIDE_HOSTNAME"]="${OVERRIDE_HOSTNAME}"
-DEFAULT_VARS["POSTMASTER_ADDRESS"]="${POSTMASTER_ADDRESS:="postmaster@domain.com"}"
 DEFAULT_VARS["POSTSCREEN_ACTION"]="${POSTSCREEN_ACTION:="enforce"}"
 DEFAULT_VARS["SPOOF_PROTECTION"]="${SPOOF_PROTECTION:="0"}"
 DEFAULT_VARS["TLS_LEVEL"]="${TLS_LEVEL:="modern"}"
@@ -416,6 +415,9 @@ function setup() {
 function _setup_default_vars() {
 	notify 'task' "Setting up default variables [$FUNCNAME]"
 
+	# update POSTMASTER_ADDRESS - must be done done after _check_hostname()
+	DEFAULT_VARS["POSTMASTER_ADDRESS"]="${POSTMASTER_ADDRESS:=postmaster@${DOMAINNAME}}"
+
 	for var in ${!DEFAULT_VARS[@]}; do
 		echo "export $var=${DEFAULT_VARS[$var]}" >> /root/.bashrc
 		[ $? != 0 ] && notify 'err' "Unable to set $var=${DEFAULT_VARS[$var]}" && kill -15 `cat /var/run/supervisord.pid` && return 1
diff --git a/test/tests.bats b/test/tests.bats
index b02e0802..27c6f790 100644
--- a/test/tests.bats
+++ b/test/tests.bats
@@ -15,7 +15,7 @@ load 'test_helper/bats-assert/load'
 }
 
 @test "checking configuration: hostname/domainname override: check container hostname is applied correctly" {
-  run docker exec mail_override_hostname /bin/bash -c "hostname | grep mail.my-domain.com"
+  run docker exec mail_override_hostname /bin/bash -c "hostname | grep unknown.domain.tld"
   assert_success
 }
 
@@ -1489,11 +1489,14 @@ load 'test_helper/bats-assert/load'
 }
 
 @test "checking dovecot: postmaster address" {
-  run docker exec mail /bin/sh -c "grep 'postmaster_address = postmaster@domain.com' /etc/dovecot/conf.d/15-lda.conf"
+  run docker exec mail /bin/sh -c "grep 'postmaster_address = postmaster@my-domain.com' /etc/dovecot/conf.d/15-lda.conf"
   assert_success
 
   run docker exec mail_with_ldap /bin/sh -c "grep 'postmaster_address = postmaster@localhost.localdomain' /etc/dovecot/conf.d/15-lda.conf"
   assert_success
+
+  run docker exec mail_override_hostname /bin/sh -c "grep 'postmaster_address = postmaster@my-domain.com' /etc/dovecot/conf.d/15-lda.conf"
+  assert_success
 }
 
 @test "checking spoofing: rejects sender forging" {