Apple Mail on Mac cannot send attachments - possible workaround

Using Apple Mail v. Version 16.0 (3776.700.51) on my M1 MacBook Pro, I have recently been unable to send email with attachments of any size, at least to certain recipients. When I tried, I got the error message, "Cannot send message using the server iCloud. Sending the message content to the server failed." I think that meant that the recipient server rejected the content (since my Connection Doctor was showing that my connection to the iCloud server was fine). My guess was that it is a security issue: attachments will not be accepted by the recipient server unless certain security-related conditions are met. But just what conditions, I asked myself...

Well, after several hours of trying to figure this out, I came upon a discussion from over a decade ago which stated that such problems can be worked around by making sure that one is using one's @iCloud address - so that the "From:" address matches the outgoing server name. Since I had been using my @me or @mac addresses, I tried using my @iCloud address instead and, voila, the content (with attachments) was accepted!

Although I haven't yet thoroughly tested this solution, I'm posting this in case you've run into the same issue, and, like me, it's stressing you out. I don't think we can blame Apple for the situation, at least if my diagnosis is correct. Rather, it may due only to the IT world's current (understandable) zealousness about security. But, if I am right, I imagine that there is a fix Apple could implement on the iCloud servers, perhaps automatically substituting @iCloud addresses for @me or @mac addresses when there are known recipient server issues. Maybe it already is doing this when one is using the iCloud.com site to send email instead of sending from one's own hardware, since the problem didn't arise for me there. Users could be made aware of the issue by Apple's providing a checkbox to enable/disable the automatic fix in Mail settings.