I don’t think the model is that far off. In real life I can read a letter and retain the contents in my mind, then burn the letter.

This letter cannot be read because it has been burnt to ash. You can only throw away the ashes. Make sure you read the letter and retain the contents in your mind, before you throw away the ashes, if you want to use them later.

But this is claiming that the letter does not exist, while allowing you to read the contents of the letter.

If it can show you the content, the container must exist!

In a post office, open a letter, burn the envelope. The content now exists, but the message does not.

but that implies the message is the envelope, which is not typically what a message means.

I would assume Outlook means that its locally-cached copy of the message exists, but the original server-side (probably IMAP) message no longer exists. And that without that message, there's no server-side resource to update — just a resource representation of a snapshot of that server-side resource, still temporarily persisted in a client-side read-through cache.

> the original server-side (probably IMAP) message no longer exists.

Doesn't Outlook rely on the Exchange mailstore?

It's a long time since I was near to Outlook and Exchange, but I thought the Exchange mailstore was some kind of X400 abomination, and that the IMAP capability was a bolt-on.

Does Outlook can even have opinions?