This is what Lawrence Finch and I have been telling y’all for quite some time, Martin_Williams:
Regardless how any given email client may choose to render (display) your received email, all files associated with your email are attachments! Pure and simple.
This is a very old part of the email Internet standards, and is highly unlikely to be changed in the future!
Additionally, as has been well demonstrated—including by way of workarounds—the problem is strictly in any email clients (Microsoft Outlook is the only one that has been demonstrated to have the issue, as far as I know) that refuse to allow you, the user, to perform bulk attachment operations simply because of how the email client has chosen to render (display) your received email.
Sure. There was a change in either the default way Apple Mail formats authored emails, or in the implementation of a newer version of the Simple Mail Transfer Protocol (SMTP) Internet standard used to transfer email from Apple Mail to your chosen SMTP email server (going to a Microsoft Exchange email server seems to be the only troublesome link, here), or both; that seems to have triggered the issue that already existed in Microsoft Outlook.
Yes. Y’all are encouraged to send Feedback to Apple, via their Feedback webpages.
However, there is simply no guarantee that changing the default authoring format, in Apple Mail, will actually solve the issue.
It might, but no guarantee!
(As for Apple changing the implementation of a newer version of the SMTP Internet standard, I highly doubt that Apple will back-out of such a change, simply because Microsoft hasn’t made the transition, yet.)
Incidentally, so long as an Android phone tries to send directly to a Microsoft Exchange email server, where the received email will be viewed by a Microsoft Outlook email client, you will, as best we’ve seen, experience the same issue.