Response status codes indicate whether a specific HTTP request has been completed. Here are the types of response codes.
With these response codes, we decide is USPS Informed delivery down or not?
If our test shows that USPS Informed delivery is up but you still can't access it then follow these tips.
If our tool shows that USPS Informed delivery is down then you can not do much to solve it. Just wait for USPS Informed delivery to solve the issue.