diff --git a/target/scripts/startup/setup.d/postfix.sh b/target/scripts/startup/setup.d/postfix.sh
index 1a6356a6..3ebdeb9d 100644
--- a/target/scripts/startup/setup.d/postfix.sh
+++ b/target/scripts/startup/setup.d/postfix.sh
@@ -119,14 +119,17 @@ function __postfix__setup_override_configuration() {
     __postfix__log 'trace' "No extra Postfix master settings loaded because optional '${OVERRIDE_CONFIG_POSTFIX_MASTER}' was not provided"
   fi
 
-  # NOTE: Must come after postfix-master.cf as custom parameter support only works provided either config references it.
+  # NOTE: `postfix-main.cf` should be handled after `postfix-master.cf` as custom parameters require an existing reference
+  # in either `main.cf` or `master.cf` prior to `postconf` reading `main.cf`, otherwise it is discarded from output.
   local OVERRIDE_CONFIG_POSTFIX_MAIN='/tmp/docker-mailserver/postfix-main.cf'
   if [[ -f ${OVERRIDE_CONFIG_POSTFIX_MAIN} ]]; then
     cat "${OVERRIDE_CONFIG_POSTFIX_MAIN}" >>/etc/postfix/main.cf
     _adjust_mtime_for_postfix_maincf
 
-    # Do not directly output to 'main.cf' as this causes a read-write-conflict
-    postconf -n >/tmp/postfix-main-new.cf 2>/dev/null
+    # Do not directly output to 'main.cf' as this causes a read-write-conflict.
+    # `postconf` output is filtered to skip expected warnings regarding overrides:
+    # https://github.com/docker-mailserver/docker-mailserver/pull/3880#discussion_r1510414576
+    postconf -n >/tmp/postfix-main-new.cf 2> >(grep -v 'overriding earlier entry')
 
     mv /tmp/postfix-main-new.cf /etc/postfix/main.cf
     _adjust_mtime_for_postfix_maincf
diff --git a/test/config/override-configs/postfix-master.cf b/test/config/override-configs/postfix-master.cf
index d284575b..f54d37d3 100644
--- a/test/config/override-configs/postfix-master.cf
+++ b/test/config/override-configs/postfix-master.cf
@@ -2,5 +2,6 @@ submission/inet/smtpd_sasl_security_options=noanonymous
 # this is a test comment, please don't delete me :'(
     # this is also a test comment, :O
 
-# `postfix-main.cf` must be processed first before this custom parameter is in scope:
+# DMS must first process `postfix-master.cf` to `master.cf` when any custom parameters are from `postfix-main.cf`
+# before an updated `main.cf` is read via `postconf`, otherwise without an existing reference the parameter is excluded.
 submission/inet/smtpd_client_restrictions=$custom_parameter
diff --git a/test/tests/parallel/set1/config_overrides.bats b/test/tests/parallel/set1/config_overrides.bats
index 2f9673ff..139765cb 100644
--- a/test/tests/parallel/set1/config_overrides.bats
+++ b/test/tests/parallel/set1/config_overrides.bats
@@ -41,17 +41,20 @@ function teardown_file() { _default_teardown ; }
 }
 
 # Custom parameter support works correctly:
-@test "Postfix - 'postfix-main.cf' should apply before 'postfix-master.cf'" {
+# NOTE: This would only fail on a fresh container state, any restart would pass successfully:
+# https://github.com/docker-mailserver/docker-mailserver/pull/3880
+@test "Postfix - 'postfix-master.cf' should apply before 'postfix-main.cf'" {
   # Retrieve the value for this setting, `postfix-master.cf` should have the override set:
   _run_in_container postconf -Ph 'submission/inet/smtpd_client_restrictions'
   assert_success
+  refute_output --partial 'postconf: warning: /etc/postfix/master.cf: undefined parameter: custom_parameter'
   asset_output '$custom_parameter'
 
-  # As it's a custom parameter ($ prefix), ensure the parameters value is correctly configured:
+  # As it's a custom parameter (`$` prefix), ensure the parameter value expands correctly:
   _run_in_container postconf -Phx 'submission/inet/smtpd_client_restrictions'
   assert_success
+  refute_output --partial 'postconf: warning: /etc/postfix/master.cf: undefined parameter: custom_parameter'
   assert_output 'cidr:{{!172.16.0.42 REJECT}}, permit_sasl_authenticated, reject'
-  refute_output 'postconf: warning: /etc/postfix/master.cf: undefined parameter: custom_parameter'
 }
 
 @test "Dovecot - 'dovecot.cf' overrides applied to '/etc/dovecot/local.conf'" {