Mail cannot save information about your mailboxes because there isn't enough space in your home folder

I agree.

Unfortunately the original choice of "Solved" by the OP cannot be changed. Sometimes better solutions come along later but the OP has no power to change it.

Apple mods can mark it as "Apple Recommended" if they come across it as they sweep through.

Did I say I was the middle of a project?

I installed Catalina only after C1 said it was now compatible, I doubt they knew of this fusion drive issue.

Also I can still use C1 but maybe once a day it packs up with a message hinting at same issue as that of Mail, also it seems to keep all my edits even with the crash.

I agree on the consequences of filling up the system drive fast. I already got the bitter taste of this just today!

I had to do a backup and restore exercise with my 64GB iPad Pro as advised by an Apple support representative(I hope you are reading this, Rebecca!) in order to troubleshoot a “battery draining too fast” issue. Every time I tried to restore my backup it failed because during the restore process my system drive just filled up (no idea why it did this, since it was supposed to copy the files to the iPad and not my system drive) and I got an error that said “restore failed due to not being able to read/write to the iPad” (or something like this). I had to delete all my Adobe CC apps and generally strip down whatever I can from my system drive in order to complete the iPad restore process. I was able to finally restore the backup but this got me into another issue. I really wish I never listened to that backup/restore advise. Now I am really frustrated with Apple, with their file system bugs, and with the kind of support I got. Really, really frustrated I am. Dang. I will definitely stop recommending Apple to my friends and colleagues now. Apple fan boy no more either! (Angry emoticon inserted here!)

Okay I have read through this entire thread and it is 01-13-20 and I am getting this same error message. I am NOT going to follow 'Charlie's' recommendation which sounds draconian.

This is nonsense. I get automatic updates and now my email is being held hostage - we need a fix!

I feel your pain, interesting to note that this post is second most commented on in the Catalina forum and still nothing is being done by Apple, so it does not assure me that they pay that much attention to them.

The most popular post is about the grief people are going through when reinstalling Catalina, so forgive me for not wanting to risk subscribing to yet another thread, just because that seems to be the only way to cure the problem on this one!

I have about 20 home mail boxes. Please indicate if you solution does not alter existing home mail box configurations and keeps data. Otherwise I am hesitant to pursue this strategy. I have seen a number of different strategies to correct this issue, spanning different iterations of os operating systems. This appears to be a systemic problem that Apple has not addressed. Currently my ability to access saved emails and generate email is being compromised.

I need suggestions for backing up my local home mailbox folders with data, the ability to retrieve.this information. And a strategy to get my mail app running angina. I have sufficient space, this is a software glitch.

I tried step three but this basically removes all of your local mail folders on you iMac. How would you then reinstall all of the local mail folders with stored email?

I ended up replacing the desktop file back to its original place and then restarted the mail program and had all of my local folders. Unfortunately, the same error message reappears in the matter of a few minutes.

I still do not see a solution to this issue and it currently impacts my ability to manage email.

who do we need to contact to escalate this issue to Apple support as a software systems issue?

Resetting the Mail settings using this approach effectively removes all existing local mail folders with saved emails that you might have had. Therefore I do not see this as an acceptable solution since it does not restore the prior configurations of mail folders and data you might have had before this error message appeared.

This solution may remove the error message but it does so at the sake of loosing all stored local email in local mailbox folders.

I trust this makes sense.

Not convinced deleting that preference list will delete any On My Mac mailboxes or POP mails. (Ie locally stored)

Have you proved this?

It might remove IMAP folders but that is no problem as they only reflect your webmail databases

I have tried this by moving the plist file to desktop, then Restarting email. My local email folders (e.g. mailboxes) were missing. Since I do not know from this point how to restore those folders and files, I closed the email app and then replaced the plist file with the older plist file that was saved on my desktop.

if someone know how to restore local mail box folders after replacing the plist file, I am listening. Otherwise this solution defeats the goal of restoring my email and locally archived email messages.

Okay Charlie...(1) I went to System Preferences>Internet Accounts and disabled all Mail on the several accounts, then (2) I followed step 3 from the referenced post. (3) I started up my mail app. All my 40 of my original local mail folders were present in the mail app, (4) I enabled the email accounts... still get the error message.

Hi again. The solution provided by re5i5tor is THE SOLUTION and not at all “draconian”. I have done it somewhere in December and I now have a stable and working machine with none of the aforementioned issues! If you have a fusion drive: follow the steps re5i5tor gave. Just back up and do it! It is not “draconian” and it is not difficult! This is the 3rd time I am posting to confirm that this is the correct solution! Thank you and good luck!

I've just installed Catalina 10.15.3 and things seem stable so far. I have a fusion drive as well. I'll post again if there are any issues. Can't believe it took 3 updates to sort out such major problems.

The article you reference states at the beginning of the article: If your Fusion Drive appears as two drives instead of one in the Finder, it's no longer working as a Fusion Drive. Here's how to fix it....

My fusion drive appears as one drive on my iMac, therefore I do not see this as a logical solution. As I said, you need to provide additional statements to buttress your argument that I need to reformat my hard drive to due an issue associated with the email app.

Firstly if there is an Apple support article I don't need to buttress anything as it trumps all argument.

Secondly I didn't say it was the solution to a Mail problem, I said it is *the* solution to a split fusion drive where the small SSD part cannot hold all your ~/Library without filling up.