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

Same here : "Am not saving mail to iCloud, have tons of space..." (200 GB free)

I tried "repairing" home folder permissions, no improvement.

I have the same issue. After reboot it's working but after some minutes the error message pops up again:

In addition to that: It also says "Disk full" and cancels a download in Google Chrome after opening Apple Mail.

That seems to be working fine. Thanks!

Edit: Nope. Same error appeared again...

As suggested (NikkolaPD Nov 12) here are more details of my iMac installationin

My iMac is 

iMac (27 inch, Late 2013)

MacOS Catalina 10.15.1 

Processor 3,5 GHz Quad-Core Intel Core i7

Memory 8 GB 1600 MHz DDR 

Startup disk Fusion disk consisting of 480GB SSD, 120GB Flash.    APFS formatted.

The original Fusion disk (rotating + flash) was substituted for SSD+Flash fusion by Humac Danmark (Apple Danmark) a couple of years ago.  

It was running High Sierra up to a couple of weeks ago. I had to clean install Catalina in order to upgrade.  

Catalina 10.15.1 was clean installed on the fusion disk via a bootable USB stick.

(Bootable USB stick created, Boot from USB stick, Erase and reformat with APFS the Macintosh HD volume, rebuild as Fusion volume, Migration assistant to restore sw from a Time machine backup). (see https://discussions.apple.com/thread/8551587 )

I tried the fix posted by clivesey 10th Oct 2019 1:03AM but still have the same mail problem. I have also tried clearing out all my mails in all my accounts (iCloud mail; gmail, hotmail) and applying the fix again. Still same problem. I have lots of space on my mac ( 64GB available of a 600GB SSD/flash 'fusion' drive) and am using iCloud storage where I also have tons of available space (1,8TB available!). Hope there comes a Catalina fix soon addressing this problem.

I'm having the same issues Email not working right stating not enough space, Since updating to Catalina, Even though apps have full disc permissions.

Sorry too late to fix typos

see also https://support.apple.com/en-gb/HT207584 for option 2

I wasn't talking about mid project upgrades to you leex.

see it says "in response to efi-123"

"...interesting to note that this post is second most commented on in the Catalina forum..."

er, what??

well how about making it more public, say on Twitter? Some bad publicity might distract them from counting all that cash

On My Mac, POP or IMAP?

Peter - You need to elaborate. I have two pop email accounts that I download in coming email to the mail app. I also have 40 local mac email folders that I move and store email that I wish to save.

I am sorry but your solution appears a bit draconian. I would be interested in knowing a bit more detail on how you came to your conclusion.

A fusion drive can't be two SSDs can it?

Cannot you install the OS directly onto the new big SSD and ignore the little one?