Blocking XML-RPC is not a great solution for fighting security risks. It’s akin to selling your car because you don’t want it to be stolen.
Your site’s XML-RPC file is kind of like a communication gateway to your site. Jetpack, the WordPress Mobile Apps, and other plugins and services will use this file to communicate to your site. If this is blocked, you will have other issues pop-up down the road for the same reasons.
If you would like to continue to only offer XML-RPC access by whitelisting IP addresses, you will need to whitelist these IP addresses:
122.248.245.244
54.217.201.243
54.232.116.4
and this range: 192.0.64.0/18
Please note that we are constantly adding new hardware to our network to keep up with demand on our services. This means that these IP addresses could change (or be added to) at any time, and is yet another reason for why we discourage restricting XML-RPC access to specific IP addresses only.