How can I fix iCloud mail sync issues on iMac and iPhone?

Product: iCloud, M3 iMac, i9 iMac, iPhone 13 Pro Max

Category: Mail > Syncing

Subject: iCloud Mail deletions not syncing across Apple devices

Message:

I’m experiencing a consistent issue where emails deleted on one Apple device reappear on others, even days later.

For example, I delete an email on my Intel iMac. The same email remains on my iPhone 16 and later shows up again on my M3 iMac. I re-delete it on each device, but it continues to resurface.

This behavior occurs even when all devices are running the latest versions of macOS and iOS, and are signed into the same iCloud account.

This is creating confusion and wasting time re-managing inbox content. I rely on iCloud Mail for daily communications, and this sync issue breaks the basic expectation that deletions are universal and permanent across devices.

Please advise if this is a known issue, or if a fix is in progress.

Eddie

[Re-Titled by Moderator]

Original Title: iCloud Mail sync bug