In all cases in which it is important for me to know whether a piece of correspondence - email or otherwise - I send is received by the intended recipient, I confirm receipt. That's the consequence of "important".
You say:
I do believe there is legislation that if an email leaves the senders server and makes it to the recipients server it is deemed to have been sent.
I'm not aware of that legislation, but let's assume it exists.
You do realise that CASA's own investigation concluded that the email in question didn't leave CASA's server? It just went in circles inside CASA.
You should read my opening post.
I'm not talking about every email. You should read my post at #7.