After a recent upgrade of Mac OS11.4, I stopped receiving all iCloud mail. However messages from both gmail and Outlook continued to come in normally. I eventually uninstalled the Apple Mail plug-in. That did not resolve the issue. I did NOT uncheck the Spam Sieve Rule in Mail Preferences, however. After spending three very long sessions online with Apple Support, I finally realized that the Rule was still checked. I unchecked it and suddenly new iCloud mail began appearing. I then reinstalled Spam Sieve, and checked the Rule for it, and mail continues to flow normally. HOWEVER… None of the mail from the past three days seems to be present anywhere. I rebuilt my mailbox as per Spam Sieve’s suggestion, but no missing email appeared. It is not present now, but also was not present previously on iCloud.com. Anyone have suggestions on where the three days of messages might be?
It sounds like you might have encountered the Mail bug where, for some users, it deletes messages instead of moving them. (To work around the bug, see #5 on this page and enable the backup feature if you want.) However, the SpamSieve rule only moves spam messages, and doesn’t touch the good ones, so the bug wouldn’t make good messages go missing unless you had another Mail rule that was moving messages from your iCloud account. If the messages were in fact deleted, they were probably not on your Mac long enough to get backed up. You might be able to ask Apple to restore a backup of your iCloud inbox, though.
Another possibility is that another of your Macs/devices moved the messages out of the iCloud account, in which case they might be in a local mailbox on that device.
Thanks for that. I’ll keep looking. Oddly, the messages would sometimes appear upon arrival, then disappear instantly.
That typically indicates that they are being moved/deleted by another device. If they were being moved by the current Mac’s rules, the messages would not appear in the inbox at all.