Mail/other apps think hard drive full, but Finder says plenty of available space. How to fix?

Phillip Breske wrote:

I found only one other report of this exact problem

I can assure you that there are thousands of identical reports.

the fix there didn't work for me. ... Deleting a bunch of files only helped a little.

Any ideas on how to clean up the hard drive so I have a useable system again?

There is no fix. You have to delete some files. I recommend keeping about 100 GB free. That will maximize the time until this happens again.

The problem here is that most of the operating system reports storage as "used" or "available". But "available" is simply made up. The only thing that matters is the amount of "free" space. When you run out of "free" space, then you get those errors.

You can delete files, but they will not be permanently removed until the operating system purges any local snapshots that keep pointers to those files. That can take a day or two. There are some 3rd party utilities that can speed up the process and give you more room right away. However, these tools can't fix the core problem. You are out of storage space. You need to delete files, move them to iCloud, or move them to an external hard drive. Note that Time Machine is a great backup system, but it is not an archive. If you want to keep the files, move them to iCloud or an external drive other than your Time Machine.

I will offer some thoughts for consideration.

• If your HD does get too full the computer can stop functioning, so this can be an important issue.
• The best way to get an accurate reading of how full the HD actually is, is by opening the Disk Utility app. It will accurately show you how much space is used and unused.
• If you are unable to delete sufficient number of files to clear needed space, try installing an external disk. Next, copy files onto it. Then you can delete those files from your HD to clear needed space. These disks are reasonably priced these days and are installed with a provided USB cable. Problem solved.