Note that you <i>also</i> have to do this step for other CAs, it&#x27;s just that browsers often cache intermediates that they&#x27;ve seen before so sites may mysteriously work for most or almost all users but fail for others if the intermediates are missing. This configuration problem is extremely common and often confusing for people to diagnose. It might be more obvious with Let&#x27;s Encrypt&#x27;s intermediate because not as many browsers have that cached yet, but the configuration issue is technically the same regardless of what CA you&#x27;re using. Sending chain files is mandatory if you want to be compatible with all user-agents that accept the root that you&#x27;re chained to.