diff --git a/test/helper/common.bash b/test/helper/common.bash
index b5e02eef..5543a20f 100644
--- a/test/helper/common.bash
+++ b/test/helper/common.bash
@@ -60,7 +60,7 @@ function __handle_container_name() {
     printf '%s' "${CONTAINER_NAME}"
     return 0
   else
-    echo 'ERROR: (helper/common.sh) Container name was either provided explicitly without the required `dms-test_` prefix, or CONTAINER_NAME is not set for implicit usage' >&2
+    echo 'ERROR: (helper/common.sh) Container name was either provided explicitly without the required "dms-test_" prefix, or CONTAINER_NAME is not set for implicit usage' >&2
     exit 1
   fi
 }
@@ -119,6 +119,27 @@ function _exec_in_container_bash() { _exec_in_container /bin/bash -c "${@}" ; }
 # @param ...  = Bash command to execute
 function _run_in_container_bash() { _run_in_container /bin/bash -c "${@}" ; }
 
+# Run a command in Bash and filter the output given a regex.
+#
+# @param ${1} = command to run in Bash
+# @param ${2} = regex to filter [OPTIONAL]
+#
+# ## Attention
+#
+# The regex is given to `grep -E`, so make sure it is compatible.
+#
+# ## Note
+#
+# If no regex is provided, this function will default to one that strips
+# empty lines and Bash comments from the output.
+function _run_in_container_bash_and_filter_output() {
+  local COMMAND=${1:?Command must be provided}
+  local FILTER_REGEX=${2:-^[[:space:]]*$|^ *#}
+
+  _run_in_container_bash "${COMMAND} | grep -E -v '${FILTER_REGEX}'"
+  assert_success
+}
+
 # ? << Functions to execute commands inside a container
 # ! -------------------------------------------------------------------
 # ? >> Functions about executing commands with timeouts
diff --git a/test/test-files/email-templates/smtp-only.txt b/test/test-files/email-templates/smtp-only.txt
index 220ace15..08288bf6 100644
--- a/test/test-files/email-templates/smtp-only.txt
+++ b/test/test-files/email-templates/smtp-only.txt
@@ -1,4 +1,4 @@
-HELO mail.localhost
+HELO mail.example.test
 MAIL FROM: test@localhost
 RCPT TO: user2@external.tld
 DATA
diff --git a/test/tests/serial/mail_quotas_disabled.bats b/test/tests/serial/mail_quotas_disabled.bats
index a012614e..bc9aa5bc 100644
--- a/test/tests/serial/mail_quotas_disabled.bats
+++ b/test/tests/serial/mail_quotas_disabled.bats
@@ -1,43 +1,33 @@
-load "${REPOSITORY_ROOT}/test/test_helper/common"
-
-# Test case
-# ---------
-# When ENABLE_QUOTAS is explicitly disabled (ENABLE_QUOTAS=0), dovecot quota must not be enabled.
+load "${REPOSITORY_ROOT}/test/helper/common"
+load "${REPOSITORY_ROOT}/test/helper/setup"
 
+BATS_TEST_NAME_PREFIX='[Quotas Disabled] '
+CONTAINER_NAME='dms-test_quotas-disabled'
 
 function setup_file() {
-  local PRIVATE_CONFIG
-  PRIVATE_CONFIG=$(duplicate_config_for_container .)
-
-  docker run -d --name mail_no_quotas \
-    -v "${PRIVATE_CONFIG}":/tmp/docker-mailserver \
-    -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
-    -e ENABLE_QUOTAS=0 \
-    -h mail.my-domain.com -t "${NAME}"
-
-  wait_for_finished_setup_in_container mail_no_quotas
+  _init_with_defaults
+  local CUSTOM_SETUP_ARGUMENTS=(--env ENABLE_QUOTAS=0)
+  _common_container_setup 'CUSTOM_SETUP_ARGUMENTS'
 }
 
-function teardown_file() {
-  docker rm -f mail_no_quotas
-}
+function teardown_file() { _default_teardown ; }
 
-@test "checking dovecot: (ENABLE_QUOTAS=0) quota plugin is disabled" {
-  run docker exec mail_no_quotas /bin/sh -c "grep '\$mail_plugins quota' /etc/dovecot/conf.d/10-mail.conf"
+@test "(Dovecot) quota plugin is disabled" {
+  _run_in_container_bash_and_filter_output 'cat /etc/dovecot/conf.d/10-mail.conf'
+  refute_output --partial 'quota'
+
+  _run_in_container_bash_and_filter_output 'cat /etc/dovecot/conf.d/20-imap.conf'
+  refute_output --partial 'imap_quota'
+
+  _run_in_container_bash "[[ -f /etc/dovecot/conf.d/90-quota.conf ]]"
   assert_failure
 
-  run docker exec mail_no_quotas /bin/sh -c "grep '\$mail_plugins imap_quota' /etc/dovecot/conf.d/20-imap.conf"
-  assert_failure
-
-  run docker exec mail_no_quotas ls /etc/dovecot/conf.d/90-quota.conf
-  assert_failure
-
-  run docker exec mail_no_quotas ls /etc/dovecot/conf.d/90-quota.conf.disab
+  _run_in_container_bash "[[ -f /etc/dovecot/conf.d/90-quota.conf.disab ]]"
   assert_success
 }
 
-@test "checking postfix: (ENABLE_QUOTAS=0) dovecot quota absent in postconf" {
-  run docker exec mail_no_quotas /bin/bash -c "postconf | grep 'check_policy_service inet:localhost:65265'"
-  assert_failure
+@test "(Postfix) Dovecot quota absent in postconf" {
+  _run_in_container postconf
+  assert_success
+  refute_output --partial "check_policy_service inet:localhost:65265'"
 }
-
diff --git a/test/tests/serial/mail_smtponly.bats b/test/tests/serial/mail_smtponly.bats
index 9549ace5..425d7008 100644
--- a/test/tests/serial/mail_smtponly.bats
+++ b/test/tests/serial/mail_smtponly.bats
@@ -1,64 +1,44 @@
-load "${REPOSITORY_ROOT}/test/test_helper/common"
+load "${REPOSITORY_ROOT}/test/helper/common"
+load "${REPOSITORY_ROOT}/test/helper/setup"
+
+BATS_TEST_NAME_PREFIX='[SMTP-Only] '
+CONTAINER_NAME='dms-test_env-smtp-only'
 
 function setup_file() {
-  docker run --rm -d --name mail_smtponly \
-    -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
-    -e SMTP_ONLY=1 \
-    -e PERMIT_DOCKER=network \
-    -e OVERRIDE_HOSTNAME=mail.my-domain.com \
-    -t "${NAME}"
+  _init_with_defaults
 
-  wait_for_finished_setup_in_container mail_smtponly
-  wait_for_smtp_port_in_container mail_smtponly
+  local CUSTOM_SETUP_ARGUMENTS=(
+    --env SMTP_ONLY=1
+    --env PERMIT_DOCKER=network
+  )
+
+  _common_container_setup 'CUSTOM_SETUP_ARGUMENTS'
+
+  _wait_for_smtp_port_in_container
 }
 
-function teardown_file() {
-  docker rm -f mail_smtponly
-}
+function teardown_file() { _default_teardown ; }
 
-#
-# configuration checks
-#
-
-@test "checking configuration: hostname/domainname override" {
-  run docker exec mail_smtponly /bin/bash -c "cat /etc/mailname | grep my-domain.com"
+@test "Dovecot quota absent in postconf" {
+  _run_in_container postconf
   assert_success
+  refute_output --partial "check_policy_service inet:localhost:65265'"
 }
 
-#
-# imap
-#
+# TODO: needs complete rework when proper DNS container is running for tests
+@test "sending mail should work" {
+  skip 'TODO: This test is absolutely broken and needs reworking!'
 
-@test "checking configuration: dovecot quota absent in postconf (disabled using SMTP_ONLY)" {
-  run docker exec mail_smtponly /bin/bash -c "postconf | grep 'check_policy_service inet:localhost:65265'"
-  assert_failure
-}
-
-#
-# smtp
-#
-
-@test "checking smtp_only: mail send should work" {
-  run docker exec mail_smtponly /bin/sh -c "postconf smtp_host_lookup=no"
   assert_success
 
-  _reload_postfix mail_smtponly
 
-  wait_for_smtp_port_in_container mail_smtponly
-  run docker exec mail_smtponly /bin/sh -c "nc 0.0.0.0 25 < /tmp/docker-mailserver-test/email-templates/smtp-only.txt"
+  # it looks as if someone tries to send mail to another domain outside of DMS
+  _run_in_container_bash "nc 0.0.0.0 25 < /tmp/docker-mailserver-test/email-templates/smtp-only.txt"
   assert_success
-  run docker exec mail_smtponly /bin/sh -c 'grep -cE "to=<user2\@external.tld>.*status\=sent" /var/log/mail/mail.log'
+  _wait_for_empty_mail_queue_in_container
+
+  # this seemingly succeeds, but looking at the logs, it doesn't
+  _run_in_container_bash 'grep -cE "to=<user2\@external.tld>.*status\=sent" /var/log/mail/mail.log'
+  # this is absolutely useless! `grep -c` count 0 but also returns 0; the mail was never properly sent!
   [[ ${status} -ge 0 ]]
 }
-
-#
-# PERMIT_DOCKER=network
-#
-
-@test "checking PERMIT_DOCKER=network: opendmarc/opendkim config" {
-  run docker exec mail_smtponly /bin/sh -c "cat /etc/opendmarc/ignore.hosts | grep '172.16.0.0/12'"
-  assert_success
-
-  run docker exec mail_smtponly /bin/sh -c "cat /etc/opendkim/TrustedHosts | grep '172.16.0.0/12'"
-  assert_success
-}
diff --git a/test/tests/serial/mail_special_use_folders.bats b/test/tests/serial/mail_special_use_folders.bats
index f5b613a6..f4be9113 100644
--- a/test/tests/serial/mail_special_use_folders.bats
+++ b/test/tests/serial/mail_special_use_folders.bats
@@ -1,40 +1,38 @@
-load "${REPOSITORY_ROOT}/test/test_helper/common"
+load "${REPOSITORY_ROOT}/test/helper/common"
+load "${REPOSITORY_ROOT}/test/helper/setup"
 
-setup_file() {
-  local PRIVATE_CONFIG
-  PRIVATE_CONFIG=$(duplicate_config_for_container .)
+BATS_TEST_NAME_PREFIX='[Special Use Folders] '
+CONTAINER_NAME='dms-test_special-use-folders'
 
-  docker run -d --name mail_special_use_folders \
-    -v "${PRIVATE_CONFIG}":/tmp/docker-mailserver \
-    -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
-    -e ENABLE_CLAMAV=0 \
-    -e ENABLE_SPAMASSASSIN=0 \
-    -e PERMIT_DOCKER=host \
-    -h mail.my-domain.com -t "${NAME}"
-
-  wait_for_smtp_port_in_container mail_special_use_folders
+function setup_file() {
+  _init_with_defaults
+  local CUSTOM_SETUP_ARGUMENTS=(--env PERMIT_DOCKER=host)
+  _common_container_setup 'CUSTOM_SETUP_ARGUMENTS'
+  _wait_for_smtp_port_in_container
 }
 
-teardown_file() {
-  docker rm -f mail_special_use_folders
-}
+function teardown_file() { _default_teardown ; }
 
-@test "checking normal delivery" {
-  run docker exec mail_special_use_folders /bin/sh -c "nc 0.0.0.0 25 < /tmp/docker-mailserver-test/email-templates/existing-user1.txt"
+@test "normal delivery works" {
+  _run_in_container_bash "nc 0.0.0.0 25 < /tmp/docker-mailserver-test/email-templates/existing-user1.txt"
   assert_success
 
-  # shellcheck disable=SC2016
-  repeat_until_success_or_timeout 30 docker exec mail_special_use_folders /bin/sh -c '[ $(ls /var/mail/localhost.localdomain/user1/new | wc -l) -eq 1 ]'
+  _count_files_in_directory_in_container /var/mail/localhost.localdomain/user1/new 1
 }
 
-@test "checking special-use folders not yet created" {
-  run docker exec mail_special_use_folders /bin/bash -c "ls -A /var/mail/localhost.localdomain/user1 | grep -E '.Drafts|.Sent|.Trash' | wc -l"
+@test "(IMAP) special-use folders should not exist yet" {
+  _run_in_container find /var/mail/localhost.localdomain/user1 -maxdepth 1 -type d
   assert_success
-  assert_output 0
+  refute_output --partial '.Drafts'
+  refute_output --partial '.Sent'
+  refute_output --partial '.Trash'
 }
 
-@test "checking special-use folders available in IMAP" {
-  run docker exec mail_special_use_folders /bin/sh -c "nc -w 8 0.0.0.0 143 < /tmp/docker-mailserver-test/nc_templates/imap_special_use_folders.txt | grep -E 'Drafts|Junk|Trash|Sent' | wc -l"
+@test "(IMAP) special-use folders should be created when necessary" {
+  _run_in_container_bash "nc -w 8 0.0.0.0 143 < /tmp/docker-mailserver-test/nc_templates/imap_special_use_folders.txt"
   assert_success
-  assert_output 4
+  assert_output --partial 'Drafts'
+  assert_output --partial 'Junk'
+  assert_output --partial 'Trash'
+  assert_output --partial 'Sent'
 }
diff --git a/test/tests/serial/mail_time.bats b/test/tests/serial/mail_time.bats
index 6bf7eb42..350880f1 100644
--- a/test/tests/serial/mail_time.bats
+++ b/test/tests/serial/mail_time.bats
@@ -1,29 +1,23 @@
-load "${REPOSITORY_ROOT}/test/test_helper/common"
+load "${REPOSITORY_ROOT}/test/helper/common"
+load "${REPOSITORY_ROOT}/test/helper/setup"
 
-setup_file() {
-  local PRIVATE_CONFIG
-  PRIVATE_CONFIG=$(duplicate_config_for_container .)
+BATS_TEST_NAME_PREFIX='[Timezone] '
+CONTAINER_NAME='dms-test_timezone'
 
-  docker run -d --name mail_time \
-    -v "${PRIVATE_CONFIG}":/tmp/docker-mailserver \
-    -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
-    -e TZ='Asia/Jakarta' \
-    -e LOG_LEVEL=debug \
-    -h mail.my-domain.com -t "${NAME}"
-
-  wait_for_smtp_port_in_container mail_time
+function setup_file() {
+  _init_with_defaults
+  local CUSTOM_SETUP_ARGUMENTS=(--env TZ='Asia/Jakarta')
+  _common_container_setup 'CUSTOM_SETUP_ARGUMENTS'
 }
 
-teardown_file() {
-  docker rm -f mail_time
-}
+function teardown_file() { _default_teardown ; }
 
-@test "checking time: setting the time with TZ works correctly" {
-  run docker exec mail_time cat /etc/timezone
+@test "setting the time with TZ works correctly" {
+  _run_in_container cat /etc/timezone
   assert_success
   assert_output 'Asia/Jakarta'
 
-  run docker exec mail_time date '+%Z'
+  _run_in_container date '+%Z'
   assert_success
   assert_output 'WIB'
 }
diff --git a/test/tests/serial/permit_docker.bats b/test/tests/serial/permit_docker.bats
index deea8082..85f00484 100644
--- a/test/tests/serial/permit_docker.bats
+++ b/test/tests/serial/permit_docker.bats
@@ -84,3 +84,12 @@ teardown_file() {
   assert_output --partial "550 5.5.1 Protocol error"
   [[ ${status} -ge 0 ]]
 }
+
+@test "checking PERMIT_DOCKER=network: opendmarc/opendkim config" {
+  skip 'TODO: this test was taken from mail_smtponly, where it did not actually belong to'
+  run docker exec mail_smtponly /bin/sh -c "cat /etc/opendmarc/ignore.hosts | grep '172.16.0.0/12'"
+  assert_success
+
+  run docker exec mail_smtponly /bin/sh -c "cat /etc/opendkim/TrustedHosts | grep '172.16.0.0/12'"
+  assert_success
+}