Mail says "Downloading" an attachment, but it doesn't download anything

Well, I'm replying to whoever is interested:

• Nothing in common with failing messages. They can come from different people who are on either GMail or iCloud email. I've seen failing attachments as .jpg, .pdf, .m4a.

• Internet speed test not applicable because a dial-up line could download 2 MB in less than 10 hours. And I now have a 200 KB file which has been downloading for over 5 minutes.

• As I said in my original post, works fine in email provider's web interface. That is in fact my workaround to download files that will not download.

• No antivirus or cleaner apps.

• And, before someone mentions it: No, I shall not try to "reset my PRAM".

Rant, sorry: I realize that not everyone is having this problem, but everyone I know is having more issues with macOS now than five years ago, and I think the reason is that instead of directing their engineers to fix reported bugs in their bug queues, Apple is instead directing their engineers to pile on more new features that no one needs (for example: Dark Mode), which instead results in even more bugs that will never be fixed as they instead move on to the next new shiny feature.

I just read about Apple's Mail Drop (https://support.apple.com/en-us/HT203093), and realized that all of the "downloading" forever messages I can recall have fairly large attachments, some MB or so, sent from iPhones. I think it is likely that, under the hood, these attachments are probably sent by Mail Drop, and therefore the trouble is probably in Mail Drop. Does anyone disagree with that?

Hello, Peter. This only occurs maybe 5% of the time, so the cause cannot be determined by A/B testing. Also, I can't imagine any setting which would intentionally cause 5% of mail attachment downloads to be extremely slow. This is clearly a bug in macOS or Mail.app.