Non-Icloud email confusion

I used to have an IPad, so set up an Icloud email account, including receiving emails from my non-Icloud email accounts (two that are with Adam internet, or iinet, or now The Messaging Company)

I was given the Ipad in 2019 and it worked well with receiving my emails while I was overseas without access to my desktop. However, eventually the battery died on the Ipad, and I haven't used it for 3 years.

Lately people sending me emails (to my @adam.com.au accounts) have been receiving bouncebacks from my redundant ICloud email account. "Mailbox Full". When I was finally able to access my ICloud account via my windows desktop, I found it had 15,500 emails dating back to 2018, as well as some photos and videos from my 2019 overseas holiday. I deleted all the emails, as these had long since been dealt with on my desktop, and most of the photos.

My Icloud storage still contains 2.9GB of emails, although I have deleted all of these, and emptied the bin.

The issue is: How do I unlink the @adam.com.au emails from the ICloud account?

There is no mail forwarding set up on my @adam accounts, not even at the host/toolbox end. I can't find anything in the icloud settings that points towards receiving my @adam emails.

I don't want to close my icloud account (for now), and I won't be closing my other email accounts. I merely want ICloud to stop butting in!

Surely there has to be a simple solution?