diff --git a/src/wp-includes/ms-default-filters.php b/src/wp-includes/ms-default-filters.php
index d0054b502e..042751e491 100644
--- a/src/wp-includes/ms-default-filters.php
+++ b/src/wp-includes/ms-default-filters.php
@@ -31,6 +31,7 @@ add_action( 'network_site_new_created_user', 'wp_send_new_user_notifications' );
 add_action( 'network_site_users_created_user', 'wp_send_new_user_notifications' );
 add_action( 'network_user_new_created_user', 'wp_send_new_user_notifications' );
 add_filter( 'sanitize_user', 'strtolower' );
+add_action( 'deleted_user', 'wp_delete_signup_on_user_delete', 10, 3 );
 
 // Roles.
 add_action( 'switch_blog', 'wp_switch_roles_and_user', 1, 2 );
diff --git a/src/wp-includes/ms-functions.php b/src/wp-includes/ms-functions.php
index c2af99ef55..9707818787 100644
--- a/src/wp-includes/ms-functions.php
+++ b/src/wp-includes/ms-functions.php
@@ -1276,6 +1276,21 @@ function wpmu_activate_signup( $key ) {
 	);
 }
 
+/**
+ * Deletes am associated signup entry when a user is deleted from the database.
+ *
+ * @since 5.5.0
+ *
+ * @param int      $id       ID of the user to delete.
+ * @param int|null $reassign ID of the user to reassign posts and links to.
+ * @param WP_User  $user     User object.
+ */
+function wp_delete_signup_on_user_delete( $id, $reassign, $user ) {
+	global $wpdb;
+
+	$wpdb->delete( $wpdb->signups, array( 'user_login' => $user->user_login ) );
+}
+
 /**
  * Create a user.
  *
diff --git a/tests/phpunit/tests/multisite/wpmuValidateUserSignup.php b/tests/phpunit/tests/multisite/wpmuValidateUserSignup.php
index 2187890cf8..7e0ad2750f 100644
--- a/tests/phpunit/tests/multisite/wpmuValidateUserSignup.php
+++ b/tests/phpunit/tests/multisite/wpmuValidateUserSignup.php
@@ -84,9 +84,9 @@ if ( is_multisite() ) :
 
 		public function test_should_fail_for_existing_signup_with_same_username() {
 			// Don't send notifications.
-			add_filter( 'wpmu_signup_user_notification', '__return_true' );
+			add_filter( 'wpmu_signup_user_notification', '__return_false' );
 			wpmu_signup_user( 'foo123', 'foo@example.com' );
-			remove_filter( 'wpmu_signup_user_notification', '__return_true' );
+			remove_filter( 'wpmu_signup_user_notification', '__return_false' );
 
 			$v = wpmu_validate_user_signup( 'foo123', 'foo2@example.com' );
 			$this->assertContains( 'user_name', $v['errors']->get_error_codes() );
@@ -94,9 +94,9 @@ if ( is_multisite() ) :
 
 		public function test_should_not_fail_for_existing_signup_with_same_username_if_signup_is_old() {
 			// Don't send notifications.
-			add_filter( 'wpmu_signup_user_notification', '__return_true' );
+			add_filter( 'wpmu_signup_user_notification', '__return_false' );
 			wpmu_signup_user( 'foo123', 'foo@example.com' );
-			remove_filter( 'wpmu_signup_user_notification', '__return_true' );
+			remove_filter( 'wpmu_signup_user_notification', '__return_false' );
 
 			global $wpdb;
 			$date = gmdate( 'Y-m-d H:i:s', time() - ( 2 * DAY_IN_SECONDS ) - 60 );
@@ -108,9 +108,9 @@ if ( is_multisite() ) :
 
 		public function test_should_fail_for_existing_signup_with_same_email() {
 			// Don't send notifications.
-			add_filter( 'wpmu_signup_user_notification', '__return_true' );
+			add_filter( 'wpmu_signup_user_notification', '__return_false' );
 			wpmu_signup_user( 'foo123', 'foo@example.com' );
-			remove_filter( 'wpmu_signup_user_notification', '__return_true' );
+			remove_filter( 'wpmu_signup_user_notification', '__return_false' );
 
 			$v = wpmu_validate_user_signup( 'foo2', 'foo@example.com' );
 			$this->assertContains( 'user_email', $v['errors']->get_error_codes() );
@@ -118,9 +118,9 @@ if ( is_multisite() ) :
 
 		public function test_should_not_fail_for_existing_signup_with_same_email_if_signup_is_old() {
 			// Don't send notifications.
-			add_filter( 'wpmu_signup_user_notification', '__return_true' );
+			add_filter( 'wpmu_signup_user_notification', '__return_false' );
 			wpmu_signup_user( 'foo123', 'foo@example.com' );
-			remove_filter( 'wpmu_signup_user_notification', '__return_true' );
+			remove_filter( 'wpmu_signup_user_notification', '__return_false' );
 
 			global $wpdb;
 			$date = gmdate( 'Y-m-d H:i:s', time() - ( 2 * DAY_IN_SECONDS ) - 60 );
@@ -130,6 +130,31 @@ if ( is_multisite() ) :
 			$this->assertNotContains( 'user_email', $v['errors']->get_error_codes() );
 		}
 
+		/**
+		 * @ticket 43232
+		 */
+		public function test_should_not_fail_for_data_used_by_a_deleted_user() {
+			global $wpdb;
+
+			// Don't send notifications.
+			add_filter( 'wpmu_signup_user_notification', '__return_false' );
+			add_filter( 'wpmu_welcome_user_notification', '__return_false' );
+
+			// Signup, activate and delete new user.
+			wpmu_signup_user( 'foo123', 'foo@example.com' );
+			$key  = $wpdb->get_var( "SELECT activation_key FROM $wpdb->signups WHERE user_login = 'foo123'" );
+			$user = wpmu_activate_signup( $key );
+			wpmu_delete_user( $user['user_id'] );
+
+			$valid = wpmu_validate_user_signup( 'foo123', 'foo2@example.com' );
+
+			remove_filter( 'wpmu_signup_user_notification', '__return_false' );
+			remove_filter( 'wpmu_signup_user_notification', '__return_false' );
+
+			$this->assertNotContains( 'user_name', $valid['errors']->get_error_codes() );
+			$this->assertNotContains( 'user_email', $valid['errors']->get_error_codes() );
+		}
+
 		public function test_invalid_email_address_with_no_banned_domains_results_in_error() {
 			$valid = wpmu_validate_user_signup( 'validusername', 'invalid-email' );