Mac Mail won't attach some files... my experience

I know this has been a recurring and unresolved problem for many people (myself included), and I wanted to share my experience with this and how I think I solved it—at least it seems to be resolved for me for now… til it breaks again.

So, after a recent OS update (13.6.9 (22G830)) my Apple Mail started acting weird when I would attach a PDF (or any file for that matter). I would drag a file to an email I was composing or responding to, and it would show an icon of the file I was trying to attach with a "downloading" word underneath the icon rather than a preview image of the file like I'd usually see. The icon of the file was just a phantom file... the actual file wasn't attached and the mail wouldn't send because it would tell me it's "downloading" the attachment. 

Not being able to attach a file to an email is a BIG problem for me as I need to send files to clients all the time. I worked through my problem-solving suggestions I found online… and the only thing that seemed to work was pulling the files I wanted to attach onto my desktop… quitting Mail… restarting Mail… then attaching the file to the email—which then seemed to work. If I added a second attachment, I would get the icon/downloading thing again, so I deleted that, restarted Mail again, and tried attaching the second file again… and it worked. Yikes, what an idiotic work-around for something that’s supposed to be (and always has been—til now) SO simple.

Then, that work-around started not working either, and the icon/downloading kept happen even after every Mail restart. UGH!

Since this work-around stopped working for me, I’ve been trying other solutions, and finally found something that seems to be working so far…

It started with my doing a “Rebuild” (found in the “Mailbox” menu in Mail… it’s at the bottom of the drop-down menu), which, from what I remember, didn’t fix things immediately, but may have played a part in the next step I took—which was to restart my machine (a MacBook Pro M1 Max) in “Safe Mode”. Once I was in Safe Mode, I tried attaching a PDF to an email, and it worked properly. I tried another file (a PNG I think), and another (JPG), and each worked fine. So, I figured that it must not be Mail that’s the problem, but one of my extensions that didn’t load in Safe Mode… so I figured I could reboot normally and start the tiresome process of trying to figure out which extensions was the culprit. 

But, when I rebooted normally and tried attaching files in Mail… and started working normally again… with that’s with all my various extensions loaded… and after days of use normally after the Safe Mode reboot (and not in Safe Mode), attaching files in Mail is still working normally. So, my encouragement to all who are dealing with this problem is to try rebooting in Safe Mode… see if attachments are working in that mode… reboot normally and see if the problem is fixed.

I’d be surprised if this is actually a fix to this issue… but perhaps this will hold until Apple addresses this issue in future updates. I hope this helps someone. Hope you have a great day!