Core networking
mask-api.icloud.com
mask-api.icloud.com is an iCloud Private Relay host. Apple lists it on TCP port 443 for iOS, iPadOS, macOS and visionOS, and marks it as supporting proxies.
Short answer
An iCloud Private Relay host on TCP 443. Unlike the relay hosts, Apple says that it supports proxies.
Block with care
Blocking it can stop iCloud Private Relay from working. Apple doesn't document its exact role.
- Matches
mask-api.icloud.com
A name with *. covers every name under it: *.push.apple.com matches 1-courier.push.apple.com.
What it serves
Apple's enterprise host list names mask-api.icloud.com in its iCloud section, for iCloud Private Relay.
Apple marks it as supporting proxies. The two relay hosts, mask.icloud.com, don't have that mark.
Apple doesn't say what this host does. The networkserviceproxy man page says that the daemon downloads its configuration from the internet; Apple doesn't say from which host.
Processes that use it
What breaks if you block it
Block with care
Blocking it can stop iCloud Private Relay from working. Apple doesn't document its exact role.
What breaks if you block it
- iCloud Private Relay may fail to set up or connect.
With Kilobat Pro and the network filter, you can block a host for every app or for one app: in Connections, select a connection and choose Block. Apple’s own services are never blocked by Kilobat’s Protection lists.
Notes
Kilobat doesn't guess at an undocumented host's role. This page describes only Apple's list.
To turn off Private Relay on one network, see Limit IP address tracking on a Mac.
Apple’s rules for its hosts
Apple’s list, Use Apple products on enterprise networks, says that devices open these connections, not Apple’s servers. Apple services fail any connection that uses HTTPS interception, so a proxy that inspects TLS should leave Apple’s hosts alone.
If a firewall allows hosts by name, allowing *.apple.com covers most Apple services, Apple says. A firewall that works only with addresses can allow 17.0.0.0/8 for IPv4, and 2403:300::/32, 2620:149::/32 and 2a01:b740::/32 for IPv6.
To see which app on your Mac opened a connection to this host, use Kilobat’s Connections tab, or the agent network log for AI agents.
Sources
- Apple Support: Use Apple products on enterprise networks
- networkserviceproxy(8), man page installed with macOS 27.2
Checked on 1 November 2026.