> I haven't heard about surprise-your-files-are-deleted bugs in core programs of other systems. That's a bigger show-stopper in my opinion.
I don't find your original anecdote convincing:
> A friend of mine lost a ton of messages when upgrading the OS (and therefore Mail).
E.g., what does this mean? They lost mail messages? How did they verify they had those messages before and after? E.g., file-system operations? GUI search? How much do they know about how Mail app stores message (e.g., I used to try understand this decades ago, but I expect today messages aren't even necessarily always stored locally)? How are you syncing mail messages, e.g., using native IMAP, or whatever Gmail uses, or Exchange? What's the email backend?
E.g. without deeper evidence this sounds more like a mail message indexing issue rather than a mail-messages-stored-on-disk-issue (in 2025, I'd personally have zero expectations about how Mail manages messages on disk, e.g., I'd expect local storage of message to be dynamically managed like most applications that aren't document-based use a combination of cloud functionality and local caching, e.g., found this in a quick search https://apple.stackexchange.com/questions/471801/ensure-maco...), but if you have stronger evidence I'd love to hear it. But as presented your extrapolating much stronger conclusions than are warranted by the anecdote in my opinion.
Mail deleted a large number of messages but not all of them. It was stored in files (which were smaller on disk, so not an indexing issue) and recovery required loading snapshots from Time Machine, converting to a format Thunderbird could import and transitioning to that.
You've only addressed something like 30% of the issues I asked about (although I'm honestly impressed you got that far), e.g., I wouldn't call Apple Mail an application designed to managed a collection of emails on disk. Isn't the important question here whether the emails were still stored on the server? E.g., or were they using POP?
I don't find your original anecdote convincing:
> A friend of mine lost a ton of messages when upgrading the OS (and therefore Mail).
E.g., what does this mean? They lost mail messages? How did they verify they had those messages before and after? E.g., file-system operations? GUI search? How much do they know about how Mail app stores message (e.g., I used to try understand this decades ago, but I expect today messages aren't even necessarily always stored locally)? How are you syncing mail messages, e.g., using native IMAP, or whatever Gmail uses, or Exchange? What's the email backend?
E.g. without deeper evidence this sounds more like a mail message indexing issue rather than a mail-messages-stored-on-disk-issue (in 2025, I'd personally have zero expectations about how Mail manages messages on disk, e.g., I'd expect local storage of message to be dynamically managed like most applications that aren't document-based use a combination of cloud functionality and local caching, e.g., found this in a quick search https://apple.stackexchange.com/questions/471801/ensure-maco...), but if you have stronger evidence I'd love to hear it. But as presented your extrapolating much stronger conclusions than are warranted by the anecdote in my opinion.