diff --git a/README.txt b/README.txt
index 78b0876..f7e2864 100644
--- a/README.txt
+++ b/README.txt
@@ -4,7 +4,7 @@ Tags: woocommerce, discount, email, shipping, coupon
 Requires at least: 5.8
 Tested up to: 7.1
 Requires PHP: 7.4
-Stable tag: 1.5.4
+Stable tag: 1.6.0
 WC requires at least: 6.0
 WC tested up to: 11.1.0
 License: GPLv2 or later
@@ -96,6 +96,10 @@ The most specific match wins: exact email, then domain, then partial match.
 
 == Changelog ==
 
+= 1.6.0 =
+* A shipping method a group is shown is now reserved for that group: customers who match no group no longer see it. Previously a method set up for approved addresses stayed on the checkout for everyone, so free delivery meant for one company could be chosen by anybody. Customers are never left with no shipping method at all.
+
+
 = 1.4.6 =
 * Housekeeping: the plugin's source moved to a shorter address. Updates continue to arrive as before, and nothing needs doing.
 
diff --git a/includes/class-db.php b/includes/class-db.php
index 474bfac..050f8e5 100644
--- a/includes/class-db.php
+++ b/includes/class-db.php
@@ -507,6 +507,25 @@ class WC_EDM_DB {
 		);
 	}
 
+	/**
+	 * Every shipping method any group reserves for itself.
+	 *
+	 * A "show" rule means the group sees that method. It also has to mean
+	 * nobody else does — otherwise reserving a free-delivery method for an
+	 * approved group leaves it on the checkout for every other customer, which
+	 * is what a shop notices as lost shipping revenue rather than as a bug.
+	 *
+	 * @return string[] Rate ids, e.g. "free_shipping:15".
+	 */
+	public static function restricted_shipping_methods() {
+		global $wpdb;
+		$table = self::table( 'shipping_rules' );
+
+		$ids = $wpdb->get_col( "SELECT DISTINCT shipping_method_id FROM {$table} WHERE action = 'show'" ); // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
+
+		return is_array( $ids ) ? $ids : array();
+	}
+
 	/**
 	 * Replace all shipping rules for a group.
 	 *
diff --git a/includes/class-frontend.php b/includes/class-frontend.php
index a11f002..0a39461 100644
--- a/includes/class-frontend.php
+++ b/includes/class-frontend.php
@@ -330,15 +330,25 @@ class WC_EDM_Frontend {
 	public function filter_shipping_rates( $rates, $package ) {
 		$match = $this->get_current_match();
 
-		if ( ! $match ) {
-			return $rates;
-		}
-
-		if ( 'group' === $match->assignment_type && $match->group_id ) {
+		// $match is null for a customer who matches nothing — the common case,
+		// and the one this whole method exists to constrain now.
+		if ( $match && 'group' === $match->assignment_type && $match->group_id ) {
 			$rates = $this->apply_group_shipping_rules( $rates, (int) $match->group_id );
+		} else {
+			// 🔴 Everyone else — including a matched customer whose assignment
+			// is not a group — must not see a method some group reserved.
+			//
+			// This used to return $rates untouched, and a test asserted that
+			// as intended: "an unmatched customer sees every method". It made
+			// a "show" rule a whitelist FOR THE GROUP and nothing more, so
+			// reserving free delivery for approved addresses left it on the
+			// checkout for every other customer. Reported from a live shop,
+			// where a gmail address could pick a free-delivery method meant
+			// for one company.
+			$rates = $this->remove_restricted_rates( $rates );
 		}
 
-		if ( ! empty( $match->free_shipping ) ) {
+		if ( $match && ! empty( $match->free_shipping ) ) {
 			foreach ( $rates as $rate ) {
 				$rate->set_cost( 0 );
 				$rate->set_taxes( array() );
@@ -348,6 +358,33 @@ class WC_EDM_Frontend {
 		return $rates;
 	}
 
+	/**
+	 * Remove every method some group reserved for itself.
+	 *
+	 * @param array $rates Available shipping rates.
+	 * @return array
+	 */
+	private function remove_restricted_rates( $rates ) {
+		$restricted = WC_EDM_DB::restricted_shipping_methods();
+
+		if ( empty( $restricted ) ) {
+			return $rates;
+		}
+
+		$filtered = array();
+
+		foreach ( $rates as $rate_id => $rate ) {
+			if ( ! in_array( $rate_id, $restricted, true ) ) {
+				$filtered[ $rate_id ] = $rate;
+			}
+		}
+
+		// The same guard the group rules carry: a shop that reserved every
+		// method it offers would otherwise leave an ordinary customer unable
+		// to check out at all, which is worse than the leak being fixed.
+		return empty( $filtered ) ? $rates : $filtered;
+	}
+
 	/**
 	 * Apply a group's show/hide shipping rules.
 	 *
@@ -362,8 +399,14 @@ class WC_EDM_Frontend {
 	private function apply_group_shipping_rules( $rates, $group_id ) {
 		$rules = WC_EDM_DB::get_shipping_rules( $group_id );
 
+		// 🔴 Not `return $rates` — a group with no rules of its own must still
+		// not see what ANOTHER group reserved. Same for a group carrying only
+		// "hide" rules: its own shown-set is empty, so the whitelist below
+		// never engages and every other group's reserved method would survive.
+		// The leak this fixes was reported for customers matching nothing; it
+		// existed for these two shapes as well.
 		if ( empty( $rules ) ) {
-			return $rates;
+			return $this->remove_restricted_rates( $rates );
 		}
 
 		$show = array();
@@ -379,6 +422,9 @@ class WC_EDM_Frontend {
 
 		$filtered = array();
 
+		// Reserved by some group, but not by THIS one.
+		$others = array_diff( WC_EDM_DB::restricted_shipping_methods(), $show );
+
 		foreach ( $rates as $rate_id => $rate ) {
 			// Whitelist mode: only explicitly shown methods survive.
 			if ( ! empty( $show ) && ! in_array( $rate_id, $show, true ) ) {
@@ -389,6 +435,10 @@ class WC_EDM_Frontend {
 				continue;
 			}
 
+			if ( in_array( $rate_id, $others, true ) ) {
+				continue;
+			}
+
 			$filtered[ $rate_id ] = $rate;
 		}
 
diff --git a/tests/smoke.php b/tests/smoke.php
index 49adf63..9f68787 100644
--- a/tests/smoke.php
+++ b/tests/smoke.php
@@ -194,9 +194,78 @@ WC()->customer->set_billing_email( 'someone@company.com' );
 $filtered = wc_edm()->frontend->filter_shipping_rates( $rates, array() );
 wc_edm_is( 'a "show" rule hides every method it does not name', array( 'flat_rate:1' ), array_keys( $filtered ) );
 
+// 🔴 This used to assert "an unmatched customer sees every method", which is
+// what made a reserved free-delivery method visible to everybody on a live
+// shop. A "show" rule now means the method belongs to that group.
 WC()->customer->set_billing_email( 'nobody@nowhere.test' );
 $filtered = wc_edm()->frontend->filter_shipping_rates( $rates, array() );
-wc_edm_is( 'an unmatched customer sees every method', 2, count( $filtered ) );
+wc_edm_is(
+	'an unmatched customer does not see a method a group reserved',
+	array( 'local_pickup:2' ),
+	array_keys( $filtered )
+);
+
+// The guard that keeps the fix from being worse than the leak: a shop that
+// reserved everything it offers must still let an ordinary customer check out.
+WC_EDM_DB::replace_shipping_rules(
+	(int) $fixtures['group_id'],
+	array(
+		array( 'shipping_method_id' => 'flat_rate:1', 'action' => 'show', 'sort_order' => 0 ),
+		array( 'shipping_method_id' => 'local_pickup:2', 'action' => 'show', 'sort_order' => 1 ),
+	)
+);
+$filtered = wc_edm()->frontend->filter_shipping_rates( $rates, array() );
+wc_edm_is( 'but is never left with no shipping at all', 2, count( $filtered ) );
+
+WC_EDM_DB::replace_shipping_rules(
+	(int) $fixtures['group_id'],
+	array( array( 'shipping_method_id' => 'flat_rate:1', 'action' => 'show', 'sort_order' => 0 ) )
+);
+
+// A SECOND group, with no rules of its own. Its members must not see what the
+// first group reserved — the leak was reported for customers matching nothing,
+// but it existed for this shape too, and for a group carrying only "hide"
+// rules, because neither engages the whitelist.
+$wc_edm_other = WC_EDM_DB::insert_group( array( 'name' => 'Ruleless', 'discount_percent' => 5 ) );
+WC_EDM_DB::insert_email(
+	array(
+		'email_pattern'   => 'ruleless@elsewhere.test',
+		'assignment_type' => 'group',
+		'group_id'        => (int) $wc_edm_other,
+		'coupon_code'     => null,
+		'custom_discount' => null,
+		'is_active'       => 1,
+		'free_shipping'   => 0,
+	)
+);
+
+WC()->customer->set_billing_email( 'ruleless@elsewhere.test' );
+$filtered = wc_edm()->frontend->filter_shipping_rates( $rates, array() );
+wc_edm_is(
+	'a group with no rules still does not see another group reserved method',
+	array( 'local_pickup:2' ),
+	array_keys( $filtered )
+);
+
+// A third rate, deliberately: with only two, hiding one and reserving the
+// other leaves nothing, the "never leave the customer without shipping" guard
+// fires, and every rate comes back — which reads as a leak but is the guard
+// working. The fixture has to leave something for the customer to be given.
+$wc_edm_rates3 = $rates;
+$wc_edm_rates3['flat_rate:9'] = new WC_Shipping_Rate( 'flat_rate:9', 'Another flat rate', 12, array(), 'flat_rate' );
+
+WC_EDM_DB::replace_shipping_rules(
+	(int) $wc_edm_other,
+	array( array( 'shipping_method_id' => 'local_pickup:2', 'action' => 'hide', 'sort_order' => 0 ) )
+);
+$filtered = wc_edm()->frontend->filter_shipping_rates( $wc_edm_rates3, array() );
+wc_edm_ok(
+	'and neither does a group carrying only hide rules',
+	! in_array( 'flat_rate:1', array_keys( $filtered ), true ),
+	'saw: ' . implode( ', ', array_keys( $filtered ) )
+);
+
+WC()->customer->set_billing_email( 'someone@company.com' );
 
 WC_EDM_DB::replace_shipping_rules( (int) $fixtures['group_id'], array() );
 
diff --git a/woocommerce-email-discount-manager.php b/woocommerce-email-discount-manager.php
index 0a6cd30..6366174 100644
--- a/woocommerce-email-discount-manager.php
+++ b/woocommerce-email-discount-manager.php
@@ -4,7 +4,7 @@
  * Plugin URI:  https://gitea.nolimit.dk/kw/woo-discount-manager
  * Update URI:  https://gitea.nolimit.dk/kw/nolimit-discounts-dist
  * Description: Apply discounts and show/hide shipping methods based on the customer's email address (full address, domain or partial match).
- * Version:     1.5.4
+ * Version:     1.6.0
  * Author:      Kristian Wind
  * Author URI:  https://gitea.nolimit.dk/kw
  * License:     GPL-2.0-or-later
@@ -28,7 +28,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 	exit;
 }
 
-define( 'WC_EDM_VERSION', '1.5.4' );
+define( 'WC_EDM_VERSION', '1.6.0' );
 define( 'WC_EDM_PLUGIN_FILE', __FILE__ );
 define( 'WC_EDM_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
 define( 'WC_EDM_PLUGIN_URL', plugin_dir_url( __FILE__ ) );