Sigh. That’s “not even wrong.” Consider:
When one financial institution needs to communicate over public networks with another such institute, they use an agreed upon process to insure the other end is who it claims to be (i.e. avoid someone intercepting and pretending to be the destination) before they exchange sensitive information. This is known as authentication (encryption is the process of hiding the exchanged information from eavesdroppers. You can authenticate without encrypting or encrypt without authenticating, but often both are done.) Email uses the same authentication protocols (this is one case where encryption was not traditionally done, though now TLS is used to encrypt.) If the sequence of bits needed to fake the authentication could be trivially created from whole cloth, the internet would cease to exist as a reliable communication medium.
So your objection is technically wrong. Nice try, counselor.
Lastly and least importantly, I have some modest expertise in this area, as I was the sole author of a product to test TLS 1.2, a version of the primary protocol used to secure web communication:
https://web.archive.org/web/20150814144639/http://iwl.com/protocol-testing/ssl-tls (Alas there aren’t a lot of customers for such a product and we never recouped development costs, so after I retired the company eventually stopped trying to sell it.)
I only responded to set the record straight on the establishment of authenticity of the email contents. I’ll let others who may be more familiar with the contents take a stab at answering your last questions.
What you are talking about is a dynamic process. This apparently involves emails that has sat in a laptop for years before allegedly being "discovered". Some may be authenticated if you can obtain other copies of the email. But is a static thing, an email is just a file. There is no imprimatur by god emblazoned on the file to prove that it is the real deal. And just because you can authenticate it, you then have to figure out what it means before using it as evidence. The justice department run by Trump's picked lap dog apparently brought no charges related to anything to do with Joe Biden. In fact, even Hunter's business seemed to only merit investigation to the extent that there might be tax fraud. That investigation is ongoing.
The most likely explanation is that Hunter Biden used his position as the son of the VP to leverage that to make money. A bit unethical IMO, but he is not the first offspring of someone famous to do that. In itself, it is not illegal.