diff --git a/src/wp-includes/comment.php b/src/wp-includes/comment.php
index 20303dc1e7e17..a29edfc4b9fe8 100644
--- a/src/wp-includes/comment.php
+++ b/src/wp-includes/comment.php
@@ -2462,25 +2462,42 @@ function wp_new_comment_notify_moderator( $comment_id ) {
 /**
  * Sends a notification of a new comment to the post author.
  *
- * @since 4.4.0
- *
  * Uses the {@see 'notify_post_author'} filter to determine whether the post author
  * should be notified when a new comment is added, overriding site setting.
  *
+ * @since 4.4.0
+ * @since 7.1.0 The comment approval status is now checked before the
+ *              {@see 'notify_post_author'} filter, and invalid comment IDs
+ *              return false without firing the filter.
+ *
  * @param int $comment_id Comment ID.
  * @return bool True on success, false on failure.
  */
 function wp_new_comment_notify_postauthor( $comment_id ) {
 	$comment = get_comment( $comment_id );
-	$is_note = ( $comment && 'note' === $comment->comment_type );
+	if ( ! ( $comment instanceof WP_Comment ) ) {
+		return false;
+	}
+	$comment_id = (int) $comment->comment_ID;
+	$is_note    = ( 'note' === $comment->comment_type );
 
-	$maybe_notify = $is_note ? get_option( 'wp_notes_notify', 1 ) : get_option( 'comments_notify' );
+	// By default, only notify for approved comments and notes.
+	if ( '1' !== $comment->comment_approved && ! $is_note ) {
+		$maybe_notify = false;
+	} elseif ( $is_note ) {
+		$maybe_notify = get_option( 'wp_notes_notify', 1 );
+	} else {
+		$maybe_notify = get_option( 'comments_notify' );
+	}
 
 	/**
-	 * Filters whether to send the post author new comment notification emails,
-	 * overriding the site setting.
+	 * Filters whether to send the post author new comment and note notification emails,
+	 * overriding the site settings and defaults. By default, notifications are sent for
+	 * all notes and for approved comments.
 	 *
 	 * @since 4.4.0
+	 * @since 7.1.0 Comment approval status is checked before this filter,
+	 *              and the filter no longer fires for invalid comment IDs.
 	 *
 	 * @param bool $maybe_notify Whether to notify the post author about the new comment.
 	 * @param int  $comment_id   The ID of the comment for the notification.
@@ -2495,13 +2512,6 @@ function wp_new_comment_notify_postauthor( $comment_id ) {
 		return false;
 	}
 
-	// Send notifications for approved comments and all notes.
-	if (
-		! isset( $comment->comment_approved ) ||
-		( '1' !== $comment->comment_approved && ! $is_note ) ) {
-			return false;
-	}
-
 	return wp_notify_postauthor( $comment_id );
 }
 
diff --git a/tests/phpunit/tests/comment.php b/tests/phpunit/tests/comment.php
index 11e78140f1020..2b7a704e2808e 100644
--- a/tests/phpunit/tests/comment.php
+++ b/tests/phpunit/tests/comment.php
@@ -1109,6 +1109,137 @@ public function test_wp_new_comment_notify_postauthor_should_not_send_email_when
 		$this->assertFalse( $sent );
 	}
 
+	/**
+	 * @ticket 64217
+	 *
+	 * @covers ::wp_new_comment_notify_postauthor
+	 */
+	public function test_wp_new_comment_notify_postauthor_filter_should_receive_false_for_unapproved_comment() {
+		$c = self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => self::$post_id,
+				'comment_approved' => '0',
+			)
+		);
+
+		update_option( 'comments_notify', 1 );
+
+		$maybe_notify = null;
+		add_filter(
+			'notify_post_author',
+			static function ( $value ) use ( &$maybe_notify ) {
+				$maybe_notify = $value;
+				return $value;
+			}
+		);
+
+		$sent = wp_new_comment_notify_postauthor( $c );
+
+		$this->assertFalse( $maybe_notify, 'The filter should receive a default of false for an unapproved comment.' );
+		$this->assertFalse( $sent, 'No notification should be sent for an unapproved comment by default.' );
+	}
+
+	/**
+	 * @ticket 64217
+	 *
+	 * @covers ::wp_new_comment_notify_postauthor
+	 */
+	public function test_wp_new_comment_notify_postauthor_filter_should_override_unapproved_comment() {
+		$c = self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => self::$post_id,
+				'comment_approved' => '0',
+			)
+		);
+
+		add_filter( 'notify_post_author', '__return_true' );
+
+		$sent = wp_new_comment_notify_postauthor( $c );
+
+		$this->assertTrue( $sent, 'The notify_post_author filter should be able to force a notification for an unapproved comment.' );
+	}
+
+	/**
+	 * @ticket 64217
+	 *
+	 * @covers ::wp_new_comment_notify_postauthor
+	 */
+	public function test_wp_new_comment_notify_postauthor_should_not_send_email_for_invalid_comment() {
+		$filter_fired = false;
+		add_filter(
+			'notify_post_author',
+			static function ( $value ) use ( &$filter_fired ) {
+				$filter_fired = true;
+				return $value;
+			}
+		);
+
+		// An empty ID such as 0 would fall back to the global comment in get_comment().
+		$sent = wp_new_comment_notify_postauthor( PHP_INT_MAX );
+
+		$this->assertFalse( $sent, 'No notification should be sent for an invalid comment ID.' );
+		$this->assertFalse( $filter_fired, 'The notify_post_author filter should not fire for an invalid comment ID.' );
+	}
+
+	/**
+	 * @ticket 64217
+	 *
+	 * @covers ::wp_new_comment_notify_postauthor
+	 */
+	public function test_wp_new_comment_notify_postauthor_filter_should_receive_truthy_default_for_unapproved_note() {
+		$c = self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => self::$post_id,
+				'comment_type'     => 'note',
+				'comment_approved' => '0',
+			)
+		);
+
+		update_option( 'wp_notes_notify', 1 );
+
+		$maybe_notify = null;
+		add_filter(
+			'notify_post_author',
+			static function ( $value ) use ( &$maybe_notify ) {
+				$maybe_notify = $value;
+				return false;
+			}
+		);
+
+		wp_new_comment_notify_postauthor( $c );
+
+		$this->assertTrue( (bool) $maybe_notify, 'The filter should receive a truthy default for an unapproved note.' );
+	}
+
+	/**
+	 * @ticket 64217
+	 *
+	 * @covers ::wp_new_comment_notify_postauthor
+	 */
+	public function test_wp_new_comment_notify_postauthor_filter_should_receive_option_value_for_approved_comment() {
+		$c = self::factory()->comment->create(
+			array(
+				'comment_post_ID' => self::$post_id,
+			)
+		);
+
+		update_option( 'comments_notify', 0 );
+
+		$maybe_notify = null;
+		add_filter(
+			'notify_post_author',
+			static function ( $value ) use ( &$maybe_notify ) {
+				$maybe_notify = $value;
+				return $value;
+			}
+		);
+
+		$sent = wp_new_comment_notify_postauthor( $c );
+
+		$this->assertFalse( (bool) $maybe_notify, 'The filter should receive the comments_notify option value as the default for an approved comment.' );
+		$this->assertFalse( $sent, 'No notification should be sent for an approved comment when comments_notify is disabled.' );
+	}
+
 	/**
 	 * @ticket 43805
 	 *