'UID COPY' (target: INBOX/.INBOX.Spam)' failed for Mailbox 'INBOX' with server error

The email message 'Welcome to Apple Support Communities!' -> ''UID COPY' (target: INBOX/.INBOX.Spam)' failed for Mailbox 'INBOX' with server error: Client tried to access nonexistent namespace (Mailbox name should probably be prefixed with: INBOX.) 

Might be related to my problem here? https://discussions.apple.com/thread/251575420

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When uploading local My Mac email archives to the IMAP server, I sometimes get a similar error when a suspected message is spam OR I get the title's error when an arriving message is considered Spam.

What is the best way to solve this? Apple Mail really isn't showing me any love :(

Thanks!

Devvie

PS:

Yes I see the irony seen whom sent the email ;-)