For iCloud Mail, ensure "Push" is enabled under Settings > Apps > Mail > Accounts > Fetch New Data . Network & Connection Requirements
APNs requires specific open ports to communicate. If you are on a restricted network (like a corporate or school Wi-Fi), ensure the following: How to Fix "Apple Push" Errors
Go to Settings > Notifications and ensure "Allow Notifications" is enabled for the specific app. For iCloud Mail, ensure "Push" is enabled under
Ensure Do Not Disturb or other Focus modes are turned off in the Control Center. For iCloud Mail
Battery-saving features can restrict background activity; turn this off in Settings > Battery .
If you are developing an app and encountering errors, verify these backend and configuration steps: Troubleshooting push notifications - Apple Developer