How to disable spam processing?

How to disable spam processing?

Several relatives and myself have setup free accounts with zoho and use Thunderbird as a POP3 client.  However quite recently emails have not been showing up and after eventually logging in to web view showed that they have gone into the spam folder - for no apparent reason.  Emails from the same (family and bank) addresses have been coming through fine, and then suddenly started being filtered into spam.  Since then one email from the same family member has got through without going into spam!

Anyway I don't want to trust this spam processing any more and so I want to turn it OFF.  However I cannot seem to turn it off.  I go to Settings and the Anti-Spam page and click the button to "Disable" "Spam Process" and it all seems good (including giving me a warning about it), but if I navigate away from the Anti-Spam page and back to it again, it has switched back to "Enable" already!

So how can I disable it and leave it disabled!?