All our servers are currently hosted on Amazon AWS eu-west-1 in Ireland. Below is a list of the IPs Hotjar uses to send egress, outgoing, traffic from which you can whitelist if required on your end.
18.203.61.76
18.203.176.135
52.17.197.221
The IPs listed above do not cover the actual domain
The actual domain is https://insights.hotjar.com. This is due to it being served by our CDN provider. We suggest to whitelist the domains *.hotjar.com especially for applying CSS to Heatmaps. This is not needed for CSS in Recordings.