Prevent BP message replies from triggering notifications

prevent-bp-message-reply-notifications.php

<?php

remove_action( 'messages_message_sent', 'messages_notification_new_message', 10 );
add_action(
	'messages_message_sent',
	function( $message ) {
		$thread_messages = BP_Messages_Thread::get_messages( $message->thread_id );
		if ( 1 === count( $thread_messages ) && $message->id === $thread_messages[0]->id ) {
			messages_notification_new_message( $message );
		}
	}
);