This weekend, Michael Tsai, the man who developed EaglerFiler and the SpamSieve plug-in for the Mac version of Apple Mail, warned macOS users that they could lose lots of data when they upgrade to macOS Catalina 10.15.0 (build 19A583).
Tsai wrote in a blog post that several users updated their Mail’s data store to Catalina from Mojave and got a message that it was successful.
However, it turned out later that numerous email messages were either completely missing or incomplete. Some users also lost message content while trying to move emails from one mailbox to another.
According to the blog, using drag-and-drop or AppleScript to move messages from one mailbox to another sometimes resulted in a blank message with only headers showing up.
Tsai continued: “If the message was moved to a server mailbox, other devices see the message as deleted.” Furthermore, syncing can spread the bug to other computers.
He added that this was a particularly serious issue, because users might not know that something went wrong until they wanted to view one of these messages.
Since email data changes all the time, trying to restore backups and then merge them with messages received after the latest backup is a nightmare.
Tsai added that Apple Support seems to be wrongly telling users that they can’t recover lost Mail data in Catalina from a Time Machine backup that was carried out via macOS Mojave.
He said that by using the File -> Import Mailboxes menu option in Apple Mail, it is possible to selectively import messages into Mail in Catalina as new local mailboxes. The exact cause of the bug remains unclear.
Apple released the beta version of macOS Catalina 10.15.1 to developers just before the weekend, but it’s unknown whether this resolves the problem. Tsai advised users not to update Catalina for now.
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