If Apple Mail is not receiving emails consistently across devices, it is usually due to iCloud sync issues, incorrect IMAP settings, or unstable internet connections on one or more devices. Outdated macOS or iOS versions, full iCloud Mail storage, or Mail rules can also cause delays or missing messages. Make sure all devices are signed in with the same Apple ID, iCloud Mail is enabled, and account settings match. Rebuilding the mailbox and updating systems often helps. To avoid data loss during sync problems, maintaining a backup with the SysInfo iCloud Backup Tool keeps your emails safe and accessible.
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