I use iCloud only for testing the iCloud sync feature of my App Store apps. As I mentioned in my recent blog post, I don’t have an iCloud email account. In System Settings, iCloud is disabled for all Mail uses. Yet when I send an email from a non‑iCloud account to another non‑iCloud account, Mail immediately triggers an iCloud connection, as shown by Little Snitch.

In testing, I’ve repeatedly reproduced this behavior. The cloudd process attempts to connect to https://gateway.icloud.com:443/ckdatabase/api/client/query/retrieve, and the nsurlsessiond process connects to https://gateway.icloud.com:443/ckdatabase/api/client/record/save, over TCP and UDP, likely falling back to the alternate seç when the first attempt is blocked. I can’t analyze the packets with Proxyman because iCloud uses certificate pinning, and a network extension can’t access unencrypted data either.

Thus, I still don’t know why Mail app queries and saves data in CloudKit when I’ve disabled Mail in iCloud. I’ve decided to create Little Snitch rules to block cloudd and nsurlsessiond from contacting gateway.icloud.com, and will temporarily disable them if I need to test iCloud sync for development.