I set up new computers somewhat frequently and have never had any issues downloading the entire 20 year old email-never-deleted mailbox from the server, including attachments.

I will also point out that free email is not something that should be expected to be a scalable storage service.

That’s interesting, maybe I’m doing something wrong

That said, the times I’ve encountered this, when the import doesn’t actually fail and appears successful, I still can’t access the specific attachment I’m looking for

It could be an old picture that is probably gone for good but forever shows loading… in the ui